Educational Side of SML

[ET1]

Many of us who enjoy shooting simply want to load a firearm with a provided safe recommended load and fire away.
Then there are those that want to produce their own safe loads through reloading and fire away.
If the word “safe” is the key element and you don’t want to look any further or deeper into using smokeless powder then enjoy your time shooting. If you desire to possibly gain more knowledge about smokeless powder then I hope to open a door of understanding that I’ve gone through.

When I purchased my 10ML-II the owner’s manual gave you a guide line of recommended powders and bullets to use which I followed faithfully for a few years to get familiar with my equipment. After a while curiosity got the better of me how we could safely use such a fast burning powder as 4759 in a 50Cal?
Savage promoted the strength of their barrels for the 10ML-II and gave you a numerical value for pressures they could withstand. Yet they never mentioned what pressures their recommended loads would generate.

What really fueled my curiosity of “what gives” was others adapting other powders and duplex loads to safely reach even more heights with velocity. I finally reached a point of “I got to know” and began doing research of “Powder Burn Rates” and “Interior Ballistics”. Eventually a picture began to take form of what is really taking place in a bore when a shot is fired. What was missing was some way to monitor and record this now known activity in the bore. Hence I acquired a Pressure Trace Unit. The unit basically removed a blind spot by providing a visual representation of what is happening with a load when fired in the bore.

First thought with the mention of a pressure trace unit is it senses the amount of pressure inside a bore. It actually does more than that by providing the powder burn rate response and amount (not peak) of pressure a bullet load is exposed to that in turn affects final velocity.
This unit to me is also like a life line warning me not to venture to far or too deep into unknown territories that can be disastrous. For the price of the unit to me it basically is like paying a tuition fee for learning and that’s never cheap these days.

Below is a PT that shows the results for the pressure cycle of a 250gr bullet/sabot in a 50Cal with a load of 43gr of the old 4759 that came in a half pound can. Underneath the trace is some info PSI, Rise and Area. Velocity input is taken from a chronograph and added to the Trace Info separately.

50-43gr 4759.JPG



Rise is the representation of the powders accelerated burn characteristic towards Peak Pressure for a specific load. There are a few more things that it can reveal but for our purpose we really don’t need to clutter our vision with them at the moment.

Area is a representation of the overall amount of pressure the bullet load is exposed to. This is important as the final resulting velocity is dictated by this factor. The larger the area-value the higher the resulting velocity.

Peak Pressure defines itself so no real explanation is needed here.

OBT Nodes (Sweet Spots) for a given load are shown as Red Diamonds along the bottom of the trace. When you follow the pressure outline you will see a small cross indicator appear on the outline indicating the bullet exit point. Here you need 2-info inputs into the program for it to appear and function.
1) The bullet depth from the muzzle.
2) The muzzle velocity of the load acquired from a chronograph.
With the above info the unit now can calculate the position for the sweet spot and exit point of the bullet load. The idea is to get the exit point directly above a node. So far it has proven to be pretty close to the sweet spot.

Any conveyed information is open to discussion or questions for clarification.

Ed

[MikePal]

For the price of the unit to me it basically is like paying a tuition fee for learning and that’s never cheap these days.

Sort of like taking a course in Automotive Engineering to understand how to make your car go faster...probably not going to pay for itself because hwy's have speed limits, but interesting to know....actually I think there are a few University degrees that could apply to

Not sure if finding a sweet spot, in terms of your PT, is of much value if your not also considering the bullet and sabot as an integral part of the end equation for achieving the best accuracy (if that is your end goal?)

...ie...Finding the perfect powder measure to attain a perfect PT without considering the max velocity for a fixed bullet/sabot combination is meaningless if that doesn't also produce the best ballistic performance (accuracy) for that bullet.

It appears a lot of guys are pushing their SML's to achieve max velocities, to the point they have exceeded the ballistic capabilities of most of the ML .45s on the market and now are forcing themselves to using duplex sabots to be able to shot smaller/lighter CF rifle bullets to handle those velocities.

Eventually you hit the "Law of diminishing returns" and what have you achieved is meaningless. Pushing a 250 gr bullet to 2,400 ft/sec flattens out the trajectory.....but taking it from -88" drop at 500 yds (at 1280 ft/sec) to say -60" drop at 500 yds achieves what ?

Sometime it makes me wonder why guys are trying to make racing cars out of pickup trucks....LOL...

Just to clarify, I'm not condemning or criticizing your efforts Ed, I find them commendable and enjoy your posts and discussions, but as you said in your opening sentence, I'm one of the ones that trust the manufactures recommendation and enjoy playing around within those guidelines (rules ?) to discover the best powder /bullet combo that provides me the best accuracy I can expect for a ML hunting out to 200 yds. It never dawned on my till I read your posts to try and turn my ML into a long range sniper rifle...I have a .303 for that

[MikePal]

Ed...I posted another thread about a product that lines the barrel with a lube that provides a 'ceramic' like coating to reduce friction of the sabot.

If in your efforts to develop a perfect PT sweet spot, for a powder/sabot/bullet combination, would using a dry lube in your barrel significantly alter the PT curve ? If the product claims to increase velocity by 2-5% would that have a significant effect on barrel pressures as there is less resistant in the load (sabot/bullet) ?

[ET1]

Mike Pal

I enjoy reading your comments and respect your point of view.
No university degree here just a grade-12 diploma but a lot of things learned from different exposures throughout my life time.

As for my eventual goal utilizing the PT unit and knowledge gained from studying Internal Ballistics is to produce some really good and desired safe loads for varying bullet weights for my SML. Along the way I have also debunked some myths that I once too was deceived by.
My goals already have been planned along with my approach to achieve them.
Major players will be my PT unit and chronograph showing me what is happening with my approach. Then applying what I learned from my study of Internal Ballistics this should help safely guide me to my goals.

I'm hoping that this early introduction will help anyone to understand some principles of smokeless powder usage and to be able to do their own analyzes when I start some PT’s later this year. Then when I share any load info I can also have some proof if they are safe loads should anyone want to venture along with their SML.

Yes I read your post on a product that reduces bore friction with ceramic usage.
Offhand I can’t see a real gain when using a plastic sabot but definitely in a rifle bore where bullet to bore contact is constant or sabotless shooting in muzzle loader.
As for your other questions I don’t have a definitive answer and can only hypothesize what the results would be. The only problem with hypothesizing is if you are proven wrong there are some sideline jumpers here waiting to pounce on your credibility. In this case I’m going to try and deny them this opportunity.

Ed

[ET1]

After rereading Mike Pal’s post the term engineering referring to technical aspect sort of hit home. When you understand a principle it no longer is complicated or confusing.
Okay I need to try to simplify a few points when looking at a PT.

So let’s start with AREA noted on the trace but first we need to understand why this is important. From Internal Ballistics we learn that a bullet is always under constant acceleration that is dependent on the remaining pressure behind it as to how fast this rate of acceleration occurs. As pressure behind the bullet begins to drop the bullet does not accelerate as fast but is still gaining velocity at a slower rate.

With a PT we can see and monitor the rate the pressure drops after it has reached its peak value. When a powder with a slower burn rate is introduced we will see that the decay of pressure behind the bullet is not as rapid as say with a faster powder that is consumed more quickly. The end result is higher velocity.
AREA on a trace is a calculated numerical value that represents the overall amount of pressure a load generates. With a higher value of AREA the more velocity is seen.

I’m going to keep RISE in a separate post to limit any confusion between the two.

Ed

[MikePal]

From Internal Ballistics we learn that a bullet is always under constant acceleration that is dependent on the remaining pressure behind it as to how fast this rate of acceleration occurs.

Ergo my question ref the inertia of the bullet/sabot. If this dry lube has coated the barrel lands with a 'ceramic' film, then the sabot/ball combination will, if performing as theorized, accelerate quicker and at the same time provide less back pressure to ensure faster ignition of the smokeless powder.

With your PT graph, you should see a shift in the point of peak pressure if you alter any aspect of the load (sabot/bullet) or the condition of the barrel; dirty or hot or lubricated etc.

[ET1]

Ergo my question ref the inertia of the bullet/sabot. If this dry lube has coated the barrel lands with a 'ceramic' film, then the sabot/ball combination will, if performing as theorized, accelerate quicker and at the same time provide less back pressure to ensure faster ignition of the smokeless powder.

With your PT graph, you should see a shift in the point of peak pressure if you alter any aspect of the load (sabot/bullet) or the condition of the barrel; dirty or hot or lubricated etc.

Mike Pal

As to the first part of your post with theorizing creating less pressure will produce a faster ignition or burn of smokeless powder, if anything it is the opposite.

Smokeless powder has to be heated to its flash point before it can ignite. By compressing the powder reducing space between granules the thermal energy is now focused in a smaller area instead of being dispersed around the grains or migrating into volumetric space in the bore. If the pressure from the primer carrying the thermal energy should say move the bullet/sabot before the powder has a good starting ignition then you are reducing the overall efficiency of the powder burn. In some cases it may not ignite especially if you using a slower powder.

When the powder ignites in a CF cartridge and begins to burn producing some pressure the bullet moves to contact the lands. By momentarily stopping here it allows the burn to accelerate developing pressure even faster before the bullet is forced into the bore. I think of this as the jump point of a powder burn when the bullet moves into the bore. This is one of the reasons I’m looking at duplex loads.

As to the second part of your post the answer is yes if you alter any aspect of the load.
For other conditions such as dirty, hot or lubricated bore conditions if it is severe enough to alter the resulting pressure then yes you will see it.


Ed

[MikePal]

and at the same time provide less back pressure that helps to ensure faster ignition of the smokeless powder.

Mike Pal

As to the first part of your post with theorizing creating less pressure will produce a faster ignition or burn of smokeless powder, if anything it is the opposite.

Yea, sorry Ed... that was a typing error...it should that said "that helps to ensure' ......it wasn't long ago in one of your other threads that I learned that smokeless powder requires pressure placed on it for better ignition. That's why I postulated that if there is less inertia on the load there would be less pressure and therefor a shift in the ignition timing.

Any idea, in terms of measured trajectory, how much a 5% increase of velocity would have on a 250 gr bullet traveling at 2000+ft/sec at 500 yds ?

[ET1]

Mike

Using the following parameters for my ballistics program say BC of .18 (250SST) with 100yd zero at 500yds:
2000fps would produce a drop of minus 204.85”
2100fps would produce a drop of minus 189.08”

Just for fun I do have info on a duplex load that would generate 2600fps with a 250SST and only increase the peak pressure by about 1500PSI. Given the above parameters a drop of only minus 124.56” should be seen.


Ed

[ET1]

RISE represents how fast pressure builds to its peak. This involves the powder’s burn rate, bullet load mass &load resistance and bore size (volumetric spacing). RISE mostly indicates a powders burn rate by its response to burn acceleration. To basically simplify this you have to understand that pressure accelerates a powder’s burn characteristics. The more pressure it is exposed to the faster the powder burns.

For muzzle loading with a sabot RISE can make a difference whether a sabot survives or shreds quicker. That marvelous piece of plastic has to deal with the oncoming pressure at a fast rate to begin with. Its ability to survive and do its job without failing IMO is also directly related to how quick the RISE is. If a faster introduction of pressure is applied to the sabot the more stress it has to endure.
RISE is assigned a numerical value where the higher the number the slower the RISE rate and the lower the number the faster the RISE rate.

A good RISE number here for sabot loads IMO would be 100 to 130.


Ed