Reloading velocity issue: I can't figure that one out!!!

Hi All,

This is the situation: I'm reloading for a 243Win and I use H4350 and some 70g Nolser and 100g Sierra.

I use 40g of H4350 for the 100g and I get a velocity of around 2930fps. Exactly what the book tells me....
I use 43, 44 and 45g of H4350 for the 70g and I get roughly 2450fps/2600fps/2700fps, so almost 800fps less than the book.

I also shot at paper around 300+ yards and the 70g was dropping much much more than what it should so I think the chronograph is not the cause.

I measured the diameter and weight of the bullet, all good.
I used the same primer, shell, measuring gauge and all......

Anyone as an idea on this matter?
Thanks

That powder isn't listed in Hodgdon manual for 243....

You sure that is the right powder you are supposed to used for 70 grain pills?

Does not seem suitable.

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Originally Posted by Big Jack

That powder isn't listed in Hodgdon manual for 243....

You sure that is the right powder you are supposed to used for 70 grain pills?

Does not seem suitable.

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Correct but it's in there and other load data book.

https://load-data.nosler.com/load-data/243-winchester/

See attached:
Attachment 35326

It could be your barrel isn't as long as test barrel and powder may not be burning completely

Quote:

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Originally Posted by Big Jack

It could be your barrel isn't as long as test barrel and powder may not be burning completely

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Good point but my barel is 22", 2" shorter than the rifle used for the test, and 1" of barrel length is roughly 50fps. Also, load with the 100g was also with a barrel 2" longer and velocity was really close from the one published.

Please, keep them coming as I really want to figure it out.
Thanks

Pressure builds quicker in barrels as projectile weight increases. Land grove diameter verses bullet diameter also plays a huge part.

Try a different powder.

Varaget.

Varget

My 223 loves CFE 223 and works well in 30-30 as well.

H4350 or IMR4350? There is a difference albeit slight. Just asking. Ive done it before.

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Originally Posted by Mr.Boiler

H4350 or IMR4350? There is a difference albeit slight. Just asking. Ive done it before.

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I use H4350.


Sent from my iPhone using Tapatalk

I always use the actual drop data to validate my MV regardless of book values. It is literally how one "trues" their dope.

On the lower velocity using more of the same powder and yet a lighter bullet thing, consider a hotter or at least a different primer. Also case capacity difference because of different bullet length, weight, profile, case empty space, seat depth, neck tension etc. can affect velocity.

I shot a 243 and reloaded for it for decades. Varget is good and I use it quite a bit. Maybe we can help if you provide more info. It does seem counter intuitive to use more powder and a lighter bullet only to get slower speeds.

Your velocity drop is due to several factors, going from a 100 gr. bullet to a 70 gr. , there is a noticeable difference in the bearing surface area of the bullet therefore you do not have as much friction and the bullet is out of the muzzle before enough pressure builds up. Shooting at dusk or twilight you will see a large muzzle flash , this is powder being burned up outside the barrel showing an inefficient powder burn and therefore causing your velocity drop .

When the firing pin hits the primer, the pressure caused by that flame alone is enough to get your bullet moving into the rifling and the subsequent burning of the powder sends it on up further till it exits, but being of light weight it has already exited before the powder has burned up completely and built up enough pressure to get the velocity you require, that is why you would see a long muzzle flash towards dark indicating an inefficient powder choice.

To get your velocity to where it should be, the powder should burn within the length of your barrel, using a light bullet and a slow burning powder doesn't allow for this to happen.
When shooting lighter bullets, you should go to a faster burning powder, varget has been suggested, myself I have had extremely accurate loads using imr 4320 powder, imr 4064 works also but is not as accurate in my rifle.
Your reloading manual will list several other powders that will give you the higher velocity that you are looking for.

This may all sound confusing, but I am having a hard time typing as I have a Gout Flare up in my right hand , and I may not be explaining things as clearly as I would like .

Quote:

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Originally Posted by jaycee

Your velocity drop is due to several factors, going from a 100 gr. bullet to a 70 gr. , there is a noticeable difference in the bearing surface area of the bullet therefore you do not have as much friction and the bullet is out of the muzzle before enough pressure builds up. Shooting at dusk or twilight you will see a large muzzle flash , this is powder being burned up outside the barrel showing an inefficient powder burn and therefore causing your velocity drop .

When the firing pin hits the primer, the pressure caused by that flame alone is enough to get your bullet moving into the rifling and the subsequent burning of the powder sends it on up further till it exits, but being of light weight it has already exited before the powder has burned up completely and built up enough pressure to get the velocity you require, that is why you would see a long muzzle flash towards dark indicating an inefficient powder choice.

To get your velocity to where it should be, the powder should burn within the length of your barrel, using a light bullet and a slow burning powder doesn't allow for this to happen.
When shooting lighter bullets, you should go to a faster burning powder, varget has been suggested, myself I have had extremely accurate loads using imr 4320 powder, imr 4064 works also but is not as accurate in my rifle.
Your reloading manual will list several other powders that will give you the higher velocity that you are looking for.

This may all sound confusing, but I am having a hard time typing as I have a Gout Flare up in my right hand , and I may not be explaining things as clearly as I would like .

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The OP has a listed load with a listed velocity for a similar barrel length, how does your post make sense when directly contradicting published data?

There are so many variables. The OP's scales could be inaccurate. He could have a long throat and pressure is being bled off before the bullets engages the rifling. Also neck tension could be loose or the bullet not crimped and not building the same pressure. And last but not least his chronograph could be the issue. They are known to be all over the place.

Sent from my SM-G925W8 using Tapatalk

Quote:

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Originally Posted by Fox

The OP has a listed load with a listed velocity for a similar barrel length, how does your post make sense when directly contradicting published data?

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By talking with people directly involved in the industry, my 59 years of reloading experience, 5 years commercially, and tons of reading about the subject [reloading] and it's variables, so that when I say something about it, I do not sound like someone who only thinks they know !

There are so many variables that in cross referencing my many reloading manuals, the published velocities for a particular caliber vary from one manual to the next.

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Originally Posted by skypilot

I always use the actual drop data to validate my MV regardless of book values. It is literally how one "trues" their dope.

On the lower velocity using more of the same powder and yet a lighter bullet thing, consider a hotter or at least a different primer. Also case capacity difference because of different bullet length, weight, profile, case empty space, seat depth, neck tension etc. can affect velocity.

I shot a 243 and reloaded for it for decades. Varget is good and I use it quite a bit. Maybe we can help if you provide more info. It does seem counter intuitive to use more powder and a lighter bullet only to get slower speeds.

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Quote:

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Originally Posted by Big Jack

Pressure builds quicker in barrels as projectile weight increases. Land grove diameter verses bullet diameter also plays a huge part.

Try a different powder.

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Quote:

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Originally Posted by jaycee

Your velocity drop is due to several factors, going from a 100 gr. bullet to a 70 gr. , there is a noticeable difference in the bearing surface area of the bullet therefore you do not have as much friction and the bullet is out of the muzzle before enough pressure builds up. Shooting at dusk or twilight you will see a large muzzle flash , this is powder being burned up outside the barrel showing an inefficient powder burn and therefore causing your velocity drop .

When the firing pin hits the primer, the pressure caused by that flame alone is enough to get your bullet moving into the rifling and the subsequent burning of the powder sends it on up further till it exits, but being of light weight it has already exited before the powder has burned up completely and built up enough pressure to get the velocity you require, that is why you would see a long muzzle flash towards dark indicating an inefficient powder choice.

To get your velocity to where it should be, the powder should burn within the length of your barrel, using a light bullet and a slow burning powder doesn't allow for this to happen.
When shooting lighter bullets, you should go to a faster burning powder, varget has been suggested, myself I have had extremely accurate loads using imr 4320 powder, imr 4064 works also but is not as accurate in my rifle.
Your reloading manual will list several other powders that will give you the higher velocity that you are looking for.

This may all sound confusing, but I am having a hard time typing as I have a Gout Flare up in my right hand , and I may not be explaining things as clearly as I would like .

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Thanks you guys!!

I really had a hard time to believe that a barrel 2” shorter in association with a light bullet and a slow powder could affect the velocity that much but now I’m pretty sure it does.

Yesterday after reading your comments I looked for a faster powder used in this reloading data that I had in stock. Sure enough I had H4895 and lots of IMR3031. So, up I went to reload 5 shells of each (36g for IMR3031 and 37g of H4895). Both chrono very close to the reloading data, around 3250fps. IMR3031 grouped alright too.

The wind died and having more time on my hand I decided to quickly load up 5 more shells of 38g of IMR3031 that I could shot over 300 yards, after all that’s why I’m working a load for. Chrono average 3312fps and group around 4.5”.

Anyway I will keep H4350 for the 100g because it groups and chrono very well but I’m going to experiment a lot more with the 70g.
It’s pretty neat to learn something!

Attachment 35340

Quote:

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Originally Posted by rippin_355

There are so many variables. The OP's scales could be inaccurate. He could have a long throat and pressure is being bled off before the bullets engages the rifling. Also neck tension could be loose or the bullet not crimped and not building the same pressure. And last but not least his chronograph could be the issue. They are known to be all over the place.

Sent from my SM-G925W8 using Tapatalk

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I had check most of these variable (scale and chrono works well), I don't crimp for my bolt action.

Quote:

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Originally Posted by Fox

The OP has a listed load with a listed velocity for a similar barrel length, how does your post make sense when directly contradicting published data?

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Sorry if I wasn't clear but my barrel is 2" shorter. I believe Jay and others were right, these 2" made a big difference in this case.
I never seen that with my 30-30 or 45-70 I assume it'sprobably because heavier bullets and faster powders are used?

Quote:

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Originally Posted by seabast

Sorry if I wasn't clear but my barrel is 2" shorter. I believe Jay and others were right, these 2" made a big difference in this case.
I never seen that with my 30-30 or 45-70 I assume it'sprobably because heavier bullets and faster powders are used?

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800fps loss for 2" is a heck of a lot

Quote:

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Originally Posted by seabast

Thanks you guys!!

I really had a hard time to believe that a barrel 2” shorter in association with a light bullet and a slow powder could affect the velocity that much but now I’m pretty sure it does.

Yesterday after reading your comments I looked for a faster powder used in this reloading data that I had in stock. Sure enough I had H4895 and lots of IMR3031. So, up I went to reload 5 shells of each (36g for IMR3031 and 37g of H4895). Both chrono very close to the reloading data, around 3250fps. IMR3031 grouped alright too.

The wind died and having more time on my hand I decided to quickly load up 5 more shells of 38g of IMR3031 that I could shot over 300 yards, after all that’s why I’m working a load for. Chrono average 3312fps and group around 4.5”.

Anyway I will keep H4350 for the 100g because it groups and chrono very well but I’m going to experiment a lot more with the 70g.
It’s pretty neat to learn something!

Attachment 35340

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Another suggestion to consider.....Load different weights of powder but same bullet and COAL(seating depth). Shoot them at 300m or yds in a true round robin manner t keep yourself unbiased and pick the load with the least vertical dispersion. Ignore the horizontal dispersion, it is likely wind.

Take the best(least vertical dispersion load) and narrow down the powder weight to be closer to either side of the best vertical dispersion load.
You are attempting to get the max SAFE velocity with the least vertical dispersion. That point will be or close to your low Statistical Deviation and most consistent MV.

That load will be the best load of that powder/bullet/primer/case/etc. for that rifle all the way to infinity. Just shoot those longer distances and record the drops.

Wind and other environmentals however are a whole other effect.

Quote:

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Originally Posted by seabast

I had check most of these variable (scale and chrono works well), I don't crimp for my bolt action.

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I reload for half a dozen 243 winchesters and you may want to give the Lee factory crimp a poke. Also seat that sucker 10 thou or so off the rifling.

Or go to the dark side and buy 87 Vmax or the other way and do 58 vmax . If you do the latter let me know I'll pull out some loads I have used that'll knock your socks off for accuracy.... those have a specific col that is nowhere near the rifling but boy do they shoot!

Quote:

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Originally Posted by Fox

800fps loss for 2" is a heck of a lot

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Hey Fox not with a slower burn powder. Seems like a lot I know but short barrels like certain powders....

Quote:

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Originally Posted by skypilot

Another suggestion to consider.....Load different weights of powder but same bullet and COAL(seating depth). Shoot them at 300m or yds in a true round robin manner t keep yourself unbiased and pick the load with the least vertical dispersion. Ignore the horizontal dispersion, it is likely wind.

Take the best(least vertical dispersion load) and narrow down the powder weight to be closer to either side of the best vertical dispersion load.
You are attempting to get the max SAFE velocity with the least vertical dispersion. That point will be or close to your low Statistical Deviation and most consistent MV.

That load will be the best load of that powder/bullet/primer/case/etc. for that rifle all the way to infinity. Just shoot those longer distances and record the drops.

Wind and other environmentals however are a whole other effect.

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That right there is the ticket.

Once you do that vary your col to fine tune further if you like.

You should be able to attain 1/2 MOA at 300 yards.

Quote:

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Originally Posted by Fox

800fps loss for 2" is a heck of a lot

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It seems a lot to me too but so far all my testing go that direction (around 30 rounds fired). I'll try that load again just to be sure though.

Quote:

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Originally Posted by skypilot

Another suggestion to consider.....Load different weights of powder but same bullet and COAL(seating depth). Shoot them at 300m or yds in a true round robin manner t keep yourself unbiased and pick the load with the least vertical dispersion. Ignore the horizontal dispersion, it is likely wind.

Take the best(least vertical dispersion load) and narrow down the powder weight to be closer to either side of the best vertical dispersion load.
You are attempting to get the max SAFE velocity with the least vertical dispersion. That point will be or close to your low Statistical Deviation and most consistent MV.

That load will be the best load of that powder/bullet/primer/case/etc. for that rifle all the way to infinity. Just shoot those longer distances and record the drops.

Wind and other environmentals however are a whole other effect.

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:thumbup:
I'm on it Boss!
Thanks

Quote:

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Originally Posted by Big Jack

I reload for half a dozen 243 winchesters and you may want to give the Lee factory crimp a poke. Also seat that sucker 10 thou or so off the rifling.

Or go to the dark side and buy 87 Vmax or the other way and do 58 vmax . If you do the latter let me know I'll pull out some loads I have used that'll knock your socks off for accuracy.... those have a specific col that is nowhere near the rifling but boy do they shoot!

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I already have the crimper but I was thinking about using later on. I just strated reloading for the 243 so I keep my focus on finding the best powder for the Nolser 70g "for my rilfe".
Thanks

Quote:

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Originally Posted by Big Jack

I reload for half a dozen 243 winchesters and you may want to give the Lee factory crimp a poke. Also seat that sucker 10 thou or so off the rifling.

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Question to you Jack: Can you really crimp if there is no crimp groove? I light crimp I assume?

Bought so Varget last night and loaded some 38, 39, 40 and 41g. Going try them in the next few days.
That reloading becomes a part time job :)

Quote:

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Originally Posted by Big Jack

Hey Fox not with a slower burn powder. Seems like a lot I know but short barrels like certain powders....

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A 22" barrel is a short barrel now? I know that longer barrels allow for a more complete burn of the powder but only to a point, even with a magnum powder. If that powder is listed for the bullet weight it should burn that powder easily within the first 18in of barrel length. I guess I am finding it really hard to believe that the 2" will give you a loss of 800fps, 80 sure but 800 seems like there is a pressure loss, either the way the bullet engages in the rifling (too narrow or too short), too far off the lands (too short) or something weird is going on with the pressure.

Quote:

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Originally Posted by seabast

Question to you Jack: Can you really crimp if there is no crimp groove? I light crimp I assume?

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There are factory crimp dies, they do not require a cannelure in the bullet, they do not roll the case mouth but squeeze in.

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Originally Posted by Fox

There are factory crimp dies, they do not require a cannelure in the bullet, they do not roll the case mouth but squeeze in.

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This is the one I have.

There is already a tight fit between the bullet and the neck so how can it crimp without a groove? Won't/Shouldn't deform the bullet.

Quote:

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Originally Posted by seabast

This is the one I have.

There is already a tight fit between the bullet and the neck so how can it crimp without a groove? Won't/Shouldn't deform the bullet.

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Read up in the die from Lee, the crimp will not wreck the bullet. That being said, if your gun is a bolt action and your neck tension is good then crimping vs not crimping may not do anything for you, it may actually hurt. There are tons of arguments about this online, I do not crimp unless it is a tube mag. My 222 I loaded to COAL on the load data and was not a fan, the next round I loaded out to fit the magazine and make sure I had 2 x the bullet diameter inside the case neck and you need a decent amount of force with a kinetic puller to remove the bullets.

Quote:

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Originally Posted by Fox

A 22" barrel is a short barrel now? I know that longer barrels allow for a more complete burn of the powder but only to a point, even with a magnum powder. If that powder is listed for the bullet weight it should burn that powder easily within the first 18in of barrel length. I guess I am finding it really hard to believe that the 2" will give you a loss of 800fps, 80 sure but 800 seems like there is a pressure loss, either the way the bullet engages in the rifling (too narrow or too short), too far off the lands (too short) or something weird is going on with the pressure.

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So, how do you explain that using two faster burning powders gave me a MV close to the reloading data? Same primer, case, rifle, OACL, setup and chrono....
Sometime , it's good to just keep his mind open, listen to others and try different things. :)

Quote:

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Originally Posted by Fox

Read up in the die from Lee, the crimp will not wreck the bullet. That being said, if your gun is a bolt action and your neck tension is good then crimping vs not crimping may not do anything for you, it may actually hurt. There are tons of arguments about this online, I do not crimp unless it is a tube mag. My 222 I loaded to COAL on the load data and was not a fan, the next round I loaded out to fit the magazine and make sure I had 2 x the bullet diameter inside the case neck and you need a decent amount of force with a kinetic puller to remove the bullets.

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I checked that a while ago and I ended knowing less than before..... Internet can make matter worse sometime....

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Originally Posted by seabast

I checked that a while ago and I ended knowing less than before..... Internet can make matter worse sometime....

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It depends on your gun and your setup, 3 rounds in 1 ragged hole at 100 yards with my 222 Rem tells me that I do not need to crimp anything to have it shoot right, your gun may not be the same but there is not really any hard and fast rule about one being better than the other. If you think about it, if you have a crimp die that will crush the neck down to a specific diameter and your neck of your brass is not uniform in thickness then you will have a different pressure applied to holding in the bullet with 2 different loads. If you just use the expanding ball on the sizing die and the diameter of the bullet then you are sizing on the inside and installing your bullet on the inside, which should be more accurate for pressure holding the bullet in the case neck. Now, if your bullets are not uniform in diameter this goes out the window. If your case necks are uniform (good brass or turned) and your bullets are mint then crimping can bump up your pressure making the body of the case a stronger pressure vessel which will cause the uniform bullet in a uniform case neck to leave the case neck at a uniform pressure and therefore have a uniform velocity with a uniform and slightly longer burn time (slower burning powder stretched out a bit).

Quote:

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Originally Posted by seabast

So, how do you explain that using two faster burning powders gave me a MV close to the reloading data? Same primer, case, rifle, OACL, setup and chrono....
Sometime , it's good to just keep his mind open, listen to others and try different things. :)

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It is not that I do not have an open mind, it is that I find it really hard to believe that 2in of barrel length will have a 30% drop in velocity.

Here is a link to a test that was done with a 308 Win.

http://bulletin.accurateshooter.com/...barrel-length/

What I am saying is that if your powder is matched to the bullet (using published data) then losing that much over 2in does not seem to click based on a lot of testing. If you are running a significantly shorter barrel like a 16in trapper 30-30, do not expect to get the same velocity of a 24in barrelled rifle but you should also not have a 30% loss in a couple inches.

Good link Fox...I see they have one for the .223 as well with basically the same loss (22-30 ft/sec) per inch.

Basically a 7% differance in of velocity between a 26" barrel and a 16.5 " barrel....

http://bulletin.accurateshooter.com/...velocity-test/

Quote:

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Originally Posted by MikePal

Good link Fox...I see they have one for the .223 as well with basically the same loss (22-30 ft/sec) per inch.

Basically a 7% differance in of velocity between a 26" barrel and a 16.5 " barrel....

http://bulletin.accurateshooter.com/...velocity-test/

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Black powder was known to take a long time to burn all the powder, this is why they had such long barrels for heavier loaded smoke poles back in the day, in the case of modern powder you can run into situations where shorter barrels actually have higher velocities if faster powders are used, but this theory for lengthening or shortening only goes so far and as you say 7% or so. The 308 test there showed a shorter bullet (110gr) having the largest velocity drop per inch but still no where near what is seen here.

Quote:

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Originally Posted by Fox

It is not that I do not have an open mind, it is that I find it really hard to believe that 2in of barrel length will have a 30% drop in velocity.

Here is a link to a test that was done with a 308 Win.

http://bulletin.accurateshooter.com/...barrel-length/

What I am saying is that if your powder is matched to the bullet (using published data) then losing that much over 2in does not seem to click based on a lot of testing. If you are running a significantly shorter barrel like a 16in trapper 30-30, do not expect to get the same velocity of a 24in barrelled rifle but you should also not have a 30% loss in a couple inches.

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As per one of my previous post 50 fps/" is what I'm used to.....
Maybe the datas are wrong, powder charge or MV?!

I shot roughly 30 rounds or so of this load. It's the drop that point me to an issue of MV and the chrono proved it. I'll will shoot an extra 5 rounds just to make sure I didn't missed something.

http://precisionrifleblog.com/2012/0...y-reliability/

Quote:

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Originally Posted by seabast

As per one of my previous post 50 fps/" is what I'm used to.....
Maybe the datas are wrong, powder charge or MV?!

I shot roughly 30 rounds or so of this load. It's the drop that point me to an issue of MV and the chrono proved it. I'll will shoot an extra 5 rounds just to make sure I didn't missed something.

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As you said "I can't figure that one out", something else wonky is going on.

What was the spread of velocity that you had? How round were the holes in the target? If you are losing 800fps and that is a legit number then something weird is going on. Have you verified the diameter of the bullet? Do you have a beam scale and a digital scale, or 2 beam scales to double check the charge weight against one another? Something is just not right here.

You are correct Fox, going from a barrel length of 24" to a 22" barrel will not account for a loss of 800fps.

I have loaded for 3 .243's with 22, 24 and 26" barrels. With same load data there was at most a 100fps difference between the 22" and the 26". Powders used are imr4350, H4350, H4895 and H4831sc. I currently load a 24" barrel for 87 and 100 grain projectiles, IMR4350 for both applications and speed values are close to published data.

Anyways, just to reiterate, 2" of barrel length is not responsible for that loss of speed

Quote:

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Originally Posted by Fox

A 22" barrel is a short barrel now? I know that longer barrels allow for a more complete burn of the powder but only to a point, even with a magnum powder. If that powder is listed for the bullet weight it should burn that powder easily within the first 18in of barrel length. I guess I am finding it really hard to believe that the 2" will give you a loss of 800fps, 80 sure but 800 seems like there is a pressure loss, either the way the bullet engages in the rifling (too narrow or too short), too far off the lands (too short) or something weird is going on with the pressure.

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No it's a combo of things for sure but slower burning powders don't work well with shorter barrels.

No it won't necessarily burn it all up in the first 18 inches either.

So yeah 2 inches plus a few other factors will result in crappy MV's

Velocity "Loss or Gain " , from Chuck Hawks site.

Of interest is the last paragraph.



Velocity loss (or gain)

It is worth noting that the velocity figures published in ammunition brochures and reloading manuals are sometimes taken in barrels different in length from those supplied on many rifles. I have seen various estimates of how much velocity is lost (or gained) when a barrel is not the same length as the test barrel in which a cartridge was chronographed. Here are some of them.

The 2001 Edition of the Shooter's Bible states, in the introduction to the Centerfire Rifle Ballistics section, "Barrel length affects velocity, and at various rates depending on the load. As a rule, figure 50 fps per inch of barrel, plus or minus, if your barrel is longer or shorter than 22 inches." However, they do not say what category of load to which this 50 fps average pertains.

Jack O'Connor wrote in The Rifle Book that, "The barrel shorter than standard has a velocity loss which averages about 25 foot-seconds for every inch cut off the barrel. Likewise, there is a velocity gain with a longer barrel." He went on to illustrate this using a .30-06 rifle shooting 180 grain bullets as an example, so his estimate was obviously for rifles in that general performance class.

Other authorities have tried to take into account the different velocity ranges within which modern cartridges operate. The Remington Catalog 2003 includes a "Centerfire Rifle Velocity Vs. Barrel Length" table that shows the following velocity changes for barrels shorter or longer than the test barrel length:

MV 2000-2500 fps, the approximate change in MV per 1" change in barrel length is 10 fps.
MV 2500-3000 fps, the approximate change in MV per 1" change in barrel length is 20 fps.
MV 3000-3500 fps, the approximate change in MV per 1" change in barrel length is 30 fps.
MV 3500-4000 fps, the approximate change in MV per 1" change in barrel length is 40 fps.
The 45th Edition of the Lyman Reloading Handbook also has a table showing Center Fire Rifle Velocity Vs. Barrel Length. Their figures apply to barrels between 20 and 26 inches in length and agree with the Remington figures. The Lyman table shows the following approximate velocity changes:

For rifles with muzzle velocities in the 1000-2000 fps range, the change in velocity for each 1" change in barrel length is 5 fps.
For rifles with muzzle velocities in the 2001-2500 fps range, the change in velocity for each 1" change in barrel length is 10 fps.
For rifles with muzzle velocities in the 2501-3000 fps range, the change in velocity for each 1" change in barrel length is 20 fps.
For rifles with muzzle velocities in the 3001-3500 fps range, the change in velocity for each 1" change in barrel length is 30 fps.
For rifles with muzzle velocities in the 3501-4000 fps range, the change in velocity for each 1" change in barrel length is 40 fps.

The 43rd edition of the Lyman reloading Handbook gave some concrete examples of velocity loss for specific calibers and loads. The Lyman technicians chronographed some high velocity cartridges in rifles with barrels ranging in length from 26 inches down to 22 inches with the following results:

The average loss for the .243 Win./100 grain bullet was 29 fps per inch.
The average loss for the .264 Win. Mag./140 grain bullet was 32 fps per inch.
The average loss for the .300 H&H Mag./220 grain bullet was 25 fps per inch.

For standard high intensity cartridges in the same test, the Lyman technicians chronographed the cartridges in barrel lengths ranging in length from 24 inches down to 20 inches with the following results:

The average loss for the .270 Win./130 grain bullet was 37 fps per inch.
The average loss for the .270 Win./150 grain bullet was 32 fps per inch.
The average loss for the .300 Sav./180 grain bullet was 17 fps per inch.
The average loss for the .30-06/180 grain bullet was 15 fps per inch.
The average loss for the .35 Rem./200 grain bullet was 11 fps per inch.

After a bunch of disclaimers, the Lyman people concluded, "The rule of thumb is that high speed, high pressure cartridges shed more speed in short barrels than do the low speed, large bore types." It's funny, but that is what I had suspected all along!

Lol what about high speed large bores....

I know with my custom smokeless muzzleloader with same load and bullet I saw a 160 fps lift in mv when going from a 26 to 28" barrel. 2505 to 2668 respectively with a 300 grain pill

But with a different bullet but same weight that difference was close to 100 feet per second difference using same powder charge....

Working with those has taught me not to make assumptions....


It all comes down to the fact that in his rifle that load stinks. If he has put the load together right there is nothing more to talk about as that is the MV for that load out of his rifle. Your 243 might act different with that load but that doesn't mean there is anything wrong with his rifle.

I'll go one further, I have seen identical Caliber rifles produce a spread of 300 fps + on same loads to Sami spec. Same range session and same batch yet individually ES was under 30....

That's why we handload. It is to tailor loads to our rifle.

Go with a better powder suited to his rifle.

I am still not convinced it was caused by barrel length or powder choice. I believe your chronograph setup was the problem. Too much sunlight or lack off can give you funky readings. Google it or read the link I posted previously.

Sent from my SM-G925W8 using Tapatalk

It has always been said, each and every rifle is different, as you have stated, " That's why we handload. It is to tailor loads to our rifle. "
My buddy and I bought two identical rifles years ago, Winchester model 70's both in .243 cal. his was faster by close to 280 fps. , till I wore out my barrel and had it re barreled with a Shilen Match Grade Barrel and a tight chamber was cut, now mine is faster than his by between 60 to 72 fps. on my Oehler Chrono.
Go figure, as has been mentioned, there are too many variables.

The first paragraph of my post above explains a lot, the loading manuals give you velocities that they/the companies got out of their barrels, that is not necessarily what you will get out of yours.

It is worth noting that the velocity figures published in ammunition brochures and reloading manuals are sometimes taken in barrels different in length from those supplied on many rifles. I have seen various estimates of how much velocity is lost (or gained) when a barrel is not the same length as the test barrel in which a cartridge was chronographed. Here are some of them.

One thing that I notice here a lot of ,is that many newcomers to reloading ask " what is your favorite load for such and such ".
One thing that I never do is state what loads I use in my rifles of any particular caliber because, "What is safe in my rifle , may be dangerous in yours ".

Of particular note, One fellow last year was on here saying I am just getting into reloading and bought such and such equipment, about a month later he was on here giving out advise on particular loads to others, which made me shake my head in disbelief.

This reminds me of a cartoon with a goofy looking guy, the caption said " six munts ago I kudn,t evun spell unjinear, now i are one ".

Just to validate much of what the experienced here have already posted AND to throw in an alternate observation which, I suppose, still validates individual barrel characteristics.....

Our department's Tango 51 builder(TacOps) did some specific testing on a .308 win barrel that was cut one inch at a time from 26" down to 22" with little change in fps. They basically cut 1" and shot ~20 rounds of Federal Factory 168gr Gold Medal Match ammo to document MV FPS. They then removed another 1" and shot 20 more rounds and repeated down to 18".

The biggest change in MV FPS that they documented was the reduction from 20" to 18" on their barrel and it was 32 FPS if I recall correctly even with or without the can.

We opted for the 18" and both had a consistent 2630 MV within ~ 5-10 fps and shot less than 1/4" at 100yd with or without the can installed. It had a 3 MOA deviation in POI from can on, to can off, yet still grouped less than 1/4".

I am interested in hearing the final poop on what specifically was found to cause a 800 fps delta.
I always shoot with my screens installed unless I use Big Jack's LabRadar but I like to loophole practice when at the farm and the screens define my loophole.

I usually get consistent MV or and error code.

Quote:

---

Originally Posted by seabast

Hi All,

This is the situation: I'm reloading for a 243Win and I use H4350 and some 70g Nolser and 100g Sierra.

I use 40g of H4350 for the 100g and I get a velocity of around 2930fps. Exactly what the book tells me....
I use 43, 44 and 45g of H4350 for the 70g and I get roughly 2450fps/2600fps/2700fps, so almost 800fps less than the book.

I also shot at paper around 300+ yards and the 70g was dropping much much more than what it should so I think the chronograph is not the cause.

I measured the diameter and weight of the bullet, all good.
I used the same primer, shell, measuring gauge and all......

Anyone as an idea on this matter?
Thanks

---

In the .243 Win. I prefer to use IMR 4064. Having said that it may be possible that the barrel on your .243 may have a different twist ratio then the gun used to establish the velocities in the manual, The variation in the twist ratio can result in a slow or fast barrel, which affects muzzle velocity. Projectile with longer bearing walls tend to give better performance in rifles with a fast twist, whereas projectile with short bearing wall give better performance in firearms with a slow twist. That aside, why is it important to match manual ballistics? In my mind, the important think is to find a load that gives consistent performance in your particular firearm, regardless of velocity. Actually lower velocity bullet that provide for consisted performance, will extend the barrel life of your firearm. Just some thoughts.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

Quote:

---

Originally Posted by Gun Nut

In the .243 Win. I prefer to use IMR 4064. Having said that it may be possible that the barrel on your .243 may have a different twist ratio then the gun used to establish the velocities in the manual, The variation in the twist ratio can result in a slow or fast barrel, which affects muzzle velocity. Projectile with longer bearing walls tend to give better performance in rifles with a fast twist, whereas projectile with short bearing wall give better performance in firearms with a slow twist. That aside, why is it important to match manual ballistics? In my mind, the important think is to find a load that gives consistent performance in your particular firearm, regardless of velocity. Actually lower velocity bullet that provide for consisted performance, will extend the barrel life of your firearm. Just some thoughts.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

---

His issue is the extreme difference, 800fps, over 2" in barrel length difference from the book numbers for the same load, not that he is not happy with the load.

Quote:

---

Originally Posted by Fox

His issue is the extreme difference, 800fps, over 2" in barrel length difference from the book numbers for the same load, not that he is not happy with the load.

---

If I can find it again Fox, I'll give you a reference for the article. In the article they were comparing the performance of .270's in relation to .30-06's. The fellow selected a number of .270's for the trial but eliminated one or two rifles because they had what he termed slow barrels. Barrel speed equates back to twist ratios, in this case it would appear that you can find rifles of the same caliber that have different twist ratio. The rifles eliminated from the trial had slow barrels, and their muzzle velocity ran well below that of the other trial firearms by a few hundred fps, and as I recall they all had equal length barrels.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

Quote:

---

Originally Posted by Fox

His issue is the extreme difference, 800fps, over 2" in barrel length difference from the book numbers for the same load, not that he is not happy with the load.

---

I found the article I was mentioning in my last posting, it was in the "Handloader's Digest, 11th. ed. In the test they started out using:
" three Remington 700s and five Winchester Model 70s, the velocity average for the same lot of ammo from the fastest barrel to the slowest one showed a loss of 250 fps. The particularly slow rifle was eliminated from our test considerations. However, such rifles do exist and are encountered not infrequently. While 270 barrels that produce higher velocities do exist, they are quite elusive. If one takes the average factory 130 grain load ( from an average barrel) and adds to it one of the frequently encountered "slow" barrels, a velocity of just over 2600 fps may be realized instead of the hoped-for 3000 fps. That's a whopping 400 fps difference."
So what determine the difference between a fast or slow barrel, the only thing I could come up with is the twist ratio of the barrel, Lyman predicates their data on a rifle with 1-10 twist/inch. but if you happen to get unlucky, you might end with a .243 with a 1-12 twist/inch, which is the twist ratio in a .308 Win. the .243's bigger brother.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

Quote:

---

Originally Posted by Gun Nut

So what determine the difference between a fast or slow barrel, the only thing I could come up with is the twist ratio of the barrel, Lyman predicates their data on a rifle with 1-10 twist/inch. but if you happen to get unlucky, you might end with a .243 with a 1-12 twist/inch, which is the twist ratio in a .308 Win. the .243's bigger brother.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

---

I do not see how twist rate will change velocity, it is the pressure behind the bullet pushing it out the barrel, if it was a smooth bore that sealed up on the bullet the velocity would be the same, twist rate causes difference in stability and therefore accuracy, not velocity.

Throat length, chamber size, throat erosion, rifling depth/bore condition, all of those things can alter velocity, again you pulled an article that says a massive change of 400fps.

The throat length can be seen when you compare 30-30 rifles and 6.5x55mm rifles. The savage 340 in 30-30 has a long throat and develops lower chamber pressure than the Winchester model 94, less pressure and therefore less velocity. The 6.5x55mm military barrels are known to have long throats to accommodate long 160gr RN bullets. This lets a short bullet like a 100gr or 120gr push out a bit before hitting the lands and essentially creates a larger pressure vessel for the powder to burn in, this lowers the pressure and velocity compared to a shorter throat barrel. This being said the throat is always the same for the same rifle and does not seem to occur the same way with new rifles based around the SAAMI chamber dimensions.

Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test)
The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book Modern Advancements in Long Range Shooting. That book includes many other fascinating field tests, including a comprehensive chronograph comparison.

Barrel Twist Rate vs. Velocity — What Tests Reveal
by Bryan Litz
When considering barrel twist rates, it’s a common belief that faster twist rates will reduce muzzle velocity. The thinking is that the faster twist rate will resist forward motion of the bullet and slow it down. There are anecdotal accounts of this, such as when someone replaces a barrel of one brand/twist with a different brand and twist and observes a different muzzle velocity. But how do you know the twist rate is what affected muzzle velocity and not the barrel finish, or bore/groove dimensions? Did you use the same chronograph to measure velocity from both barrels? Do you really trust your chronograph?

Savage Test Rifle with Six Bartlein Barrels
Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Most shooters don’t have access to the equipment required to fully explore questions like this. These are exactly the kinds of things we examine in the book Modern Advancements in Long Range Shooting. In that book, we present experiments conducted in the Applied Ballistics lab. Some of those experiments took on a “Myth Buster” tone as we sought to confirm (or deny) popular pre-conceptions. For example, here’s how we approached the question of barrel twist and muzzle velocity.

Six .308 Win Barrels from Bartlein — All Shot from the Same Rifle
We acquired six (6) barrels from the same manufacturer (Bartlein), all the same length and contour, and all chambered with the same reamer (SAAMI spec .308 Winchester). All these barrels were fitted to the same Savage Precision Target action, and fired from the same stock, and bench set-up. Common ammo was fired from all six barrels having different twist rates and rifling configurations. In this way, we’re truly able to compare what effect the actual twist rate has on muzzle velocity with a reasonable degree of confidence.

Prior to live fire testing, we explored the theoretical basis of the project, doing the physics. In this case, an energy balance is presented which predicts how much velocity you should expect to lose for a bullet that’s got a little more rotational energy from the faster twist. In the case of the .30 caliber 175 grain bullets, the math predicts a loss of 1.25 fps per inch-unit of barrel twist (e.g. a 1:8″ twist is predicted to be 1.25 fps slower than a 1:9″ twist).

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Above, data shows relationship between Twist Rate and Muzzle Velocity (MV) for various barrel twist rates and rifling types. From fast to slow, the three 1:10″ twist barrels are: 5R (canted land), 5 Groove, 5 Groove left-hand twist.
We proceeded with the testing in all 6 barrels from 1:8” to 1:12”. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the rate of approximately 1.33 fps per inch of twist. In other words, your velocity is reduced by about 5 fps if you go from a 1:12” twist to a 1:8” twist. [Editor: That’s a surprising number — much less than most folks would predict.] In this case the math prediction was pretty close, and we have to remember that there’s always uncertainty in the live fire results. Uncertainty is always considered in terms of what conclusions the results can actually support with confidence.

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied BallisticsThis is just a brief synopsis of a single test case. The coverage of twist rates in Modern Advancements in Long-Range Shooting is more detailed, with multiple live fire tests. Results are extrapolated for other calibers and bullet weights. Needless to say, the question of “how twist rate affects muzzle velocity” is fully answered.

Other chapters in the book’s twist rate section include:
· Stability and Drag – Supersonic
·

Thanks for posting that J.

Interesting article. I couldn't likely see 1.33 fps change with the chrono I own anyway.
It would be interesting to see how Brian's numbers would compare with Optimum Barrel Timing and Quick Load's barrel timing.

Quote:

---

Originally Posted by jaycee

Does Barrel Twist Rate Affect Muzzle Velocity? (Litz Test)
The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book Modern Advancements in Long Range Shooting. That book includes many other fascinating field tests, including a comprehensive chronograph comparison.

Barrel Twist Rate vs. Velocity — What Tests Reveal
by Bryan Litz
When considering barrel twist rates, it’s a common belief that faster twist rates will reduce muzzle velocity. The thinking is that the faster twist rate will resist forward motion of the bullet and slow it down. There are anecdotal accounts of this, such as when someone replaces a barrel of one brand/twist with a different brand and twist and observes a different muzzle velocity. But how do you know the twist rate is what affected muzzle velocity and not the barrel finish, or bore/groove dimensions? Did you use the same chronograph to measure velocity from both barrels? Do you really trust your chronograph?

Savage Test Rifle with Six Bartlein Barrels
Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Most shooters don’t have access to the equipment required to fully explore questions like this. These are exactly the kinds of things we examine in the book Modern Advancements in Long Range Shooting. In that book, we present experiments conducted in the Applied Ballistics lab. Some of those experiments took on a “Myth Buster” tone as we sought to confirm (or deny) popular pre-conceptions. For example, here’s how we approached the question of barrel twist and muzzle velocity.

Six .308 Win Barrels from Bartlein — All Shot from the Same Rifle
We acquired six (6) barrels from the same manufacturer (Bartlein), all the same length and contour, and all chambered with the same reamer (SAAMI spec .308 Winchester). All these barrels were fitted to the same Savage Precision Target action, and fired from the same stock, and bench set-up. Common ammo was fired from all six barrels having different twist rates and rifling configurations. In this way, we’re truly able to compare what effect the actual twist rate has on muzzle velocity with a reasonable degree of confidence.

Prior to live fire testing, we explored the theoretical basis of the project, doing the physics. In this case, an energy balance is presented which predicts how much velocity you should expect to lose for a bullet that’s got a little more rotational energy from the faster twist. In the case of the .30 caliber 175 grain bullets, the math predicts a loss of 1.25 fps per inch-unit of barrel twist (e.g. a 1:8″ twist is predicted to be 1.25 fps slower than a 1:9″ twist).

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Above, data shows relationship between Twist Rate and Muzzle Velocity (MV) for various barrel twist rates and rifling types. From fast to slow, the three 1:10″ twist barrels are: 5R (canted land), 5 Groove, 5 Groove left-hand twist.
We proceeded with the testing in all 6 barrels from 1:8” to 1:12”. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the rate of approximately 1.33 fps per inch of twist. In other words, your velocity is reduced by about 5 fps if you go from a 1:12” twist to a 1:8” twist. [Editor: That’s a surprising number — much less than most folks would predict.] In this case the math prediction was pretty close, and we have to remember that there’s always uncertainty in the live fire results. Uncertainty is always considered in terms of what conclusions the results can actually support with confidence.

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied BallisticsThis is just a brief synopsis of a single test case. The coverage of twist rates in Modern Advancements in Long-Range Shooting is more detailed, with multiple live fire tests. Results are extrapolated for other calibers and bullet weights. Needless to say, the question of “how twist rate affects muzzle velocity” is fully answered.

Other chapters in the book’s twist rate section include:
· Stability and Drag – Supersonic
·

---

Interesting article, so if it's not twist that make for the difference in velocity between a fast barrel and a slow barrel, then it's probably throat diameter. i know when the German switched from the .318 round to the .323 round, they decided to convert the older .318 to shoot the .323 round. They stop short of re-boring them, electing instead to simply enlarged the throat portion of the barrel to allow for the base swelling of the .323 round. After the bullet left the casing and stared down the bore, the short bearing wall of the .323 spritzer bullet, allowed it to travel down the .318 bore without any significant pressure increase. This would suggest that an overly generous throat diameter in a barrel could lower the pressure of internal ballistics which in turn could substantially alter (lower) muzzle velocity.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

I should have added that this is where the info came from;

We will be interviewing Bryan Litz of Applied Ballistics tomorrow at SHOT Show in Las Vegas. As a sneak preview of some of the topics we’ll cover, here are some highlights of some important, original research conducted by Bryan and his Applied Ballistics team. Bryan wanted to know how much velocity was altered by twist rate. The “real world” test results may surprise you….

The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book Modern Advancements in Long Range Shooting. That book includes many other fascinating field tests, including a comprehensive chronograph comparison.

As you can see the info came from a reliable source.

All of the twist rates for the 243 from Nosler show 1 in 10", Seabast, do you have a gun that has a non-standard twist rate? I assume not.

Hi All,
I haven't been able to check again the MV for this specific load and to be honest I haven't had time to read in details your week-end post but I'll do it all by the end of this week. Afterall, maybe the chrono was the issue that specific day.....
However, I reloaded some 70g Nosler under Varget at 100 yards and the accuracy result are alright and I haven't tried the maximum load (41g) yet. As sonn as I find the my acurate load I'll test the speed.

Quote:

---

Originally Posted by Fox

All of the twist rates for the 243 from Nosler show 1 in 10", Seabast, do you have a gun that has a non-standard twist rate? I assume not.

---

9.25" I believe

Quote:

---

Originally Posted by Fox

I do not see how twist rate will change velocity, it is the pressure behind the bullet pushing it out the barrel, if it was a smooth bore that sealed up on the bullet the velocity would be the same, twist rate causes difference in stability and therefore accuracy, not velocity.

Throat length, chamber size, throat erosion, rifling depth/bore condition, all of those things can alter velocity, again you pulled an article that says a massive change of 400fps.

The throat length can be seen when you compare 30-30 rifles and 6.5x55mm rifles. The savage 340 in 30-30 has a long throat and develops lower chamber pressure than the Winchester model 94, less pressure and therefore less velocity. The 6.5x55mm military barrels are known to have long throats to accommodate long 160gr RN bullets. This lets a short bullet like a 100gr or 120gr push out a bit before hitting the lands and essentially creates a larger pressure vessel for the powder to burn in, this lowers the pressure and velocity compared to a shorter throat barrel. This being said the throat is always the same for the same rifle and does not seem to occur the same way with new rifles based around the SAAMI chamber dimensions.

---

Fox I have two Model 336 Marlin 30-30's one built before micro-grooving, the other with micro-grooving. The older handle cast bullets like a charm. The one with the micro-grooving scatters cast all over the map. What I’ve found to date is that the older rifle is extremely tight chambered and bullets have to be sized to .308 or they won’t chamber. In the newer rifle I’m able to chamber .309 sized bullet with no effort, and I’ve even contemplated picking up a lube/sizer to try a .310 size bullets. This current thread has reignited my thoughts on what might be causing the micro-groove rifle to scatter cast about. I was blaming it on the depth of the micro-grooves .002 as opposed to traditional grove depth of .004. It may not be the micro-grooving at all, but rather a substantial drop in projectile velocity do to the larger throat diameter. The spin on a bullet is the product of two variable the rifling and the velocity at which the bullet travels through the rifling. The loads I use to propel the cast bullet pushes it close to 2000 fps and works well in the older Marlin. In the newer Marlin with it lager diameter throat the velocity could be falling of substantially so the bullet is not traveling fast enough for the rifling to provide adequate spin to stabilize it. I once had stability problems with a cast .303 bullet, it would continually key-hole with the fast burning powder load given in the manual. Then I read somewhere about using a reduced load of medium burning power, so I tried it and it straighten the bullet right out. Since than I’ve pretty much stuck to using the medium burning powdes when shooting cast.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

Quote:

---

Originally Posted by Gun Nut

In the .243 Win. I prefer to use IMR 4064. Having said that it may be possible that the barrel on your .243 may have a different twist ratio then the gun used to establish the velocities in the manual, The variation in the twist ratio can result in a slow or fast barrel, which affects muzzle velocity. Projectile with longer bearing walls tend to give better performance in rifles with a fast twist, whereas projectile with short bearing wall give better performance in firearms with a slow twist. That aside, why is it important to match manual ballistics? In my mind, the important think is to find a load that gives consistent performance in your particular firearm, regardless of velocity. Actually lower velocity bullet that provide for consisted performance, will extend the barrel life of your firearm. Just some thoughts.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

---

Thanks for the information.

To answer your question, it's because this is the first time a load is so far away from the MV book and I'm trying to figure out is I'm doing something wrong or not. Everything started trying to match the performance of the Hornady 75g....

Quote:

---

Originally Posted by Gun Nut

Fox I have two Model 336 Marlin 30-30's one built before micro-grooving, the other with micro-grooving. The older handle cast bullets like a charm. The one with the micro-grooving scatters cast all over the map. What I’ve found to date is that the older rifle is extremely tight chambered and bullets have to be sized to .308 or they won’t chamber. In the newer rifle I’m able to chamber .309 sized bullet with no effort, and I’ve even contemplated picking up a lube/sizer to try a .310 size bullets. This current thread has reignited my thoughts on what might be causing the micro-groove rifle to scatter cast about. I was blaming it on the depth of the micro-grooves .002 as opposed to traditional grove depth of .004. It may not be the micro-grooving at all, but rather a substantial drop in projectile velocity do to the larger throat diameter. The spin on a bullet is the product of two variable the rifling and the velocity at which the bullet travels through the rifling. The loads I use to propel the cast bullet pushes it close to 2000 fps and works well in the older Marlin. In the newer Marlin with it lager diameter throat the velocity could be falling of substantially so the bullet is not traveling fast enough for the rifling to provide adequate spin to stabilize it. I once had stability problems with a cast .303 bullet, it would continually key-hole with the fast burning powder load given in the manual. Then I read somewhere about using a reduced load of medium burning power, so I tried it and it straighten the bullet right out. Since than I’ve pretty much stuck to using the medium burning powdes when shooting cast.

You don't stop hunting because you grow old. You grow old because you stop hunting.
- Gun Nut

---

The micro-groove issue is a known one to cast shooters, the lead is a lot softer, even with a hard alloy, than the jacketed bullet. the cast lead bullet is sliding over the rifling rather than cutting into the rifling. The micro groove is known though to get more velocity from the same jacketed bullet as the older traditional rifling and also do that at a lower pressure, there is less resistance to the pushing into the rifling.

I think in this case the only way to compare apples to apples is to shoot the old one with factory jacketed over a chronograph and the same with the new one. Then shoot identical cast bullets in both over the chronograph and compare, your velocity difference between the 2 loads will probably be very close, meaning if the micro groove is 100fps higher with cast over the traditional then it will probably be the same with the cast, assume the bullet sizes are the same and the loads are the same.

The throat can have an impact for sure, but size your cast to .308 or .309 and try them and see, you will not know based on where the bullet hits compared to what the gun was sighted in for, numbers are the only things you can measure.