Dealing with Bore Heat and Sabots

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November 26th, 2021, 08:43 AM
impact

Quote:

Originally Posted by MikePal

It's a two-way cup, either side up/down. ..so yes the primary purpose is to prevent the gas from seeping around the ball.

They didn't do very well marketing these as guys were concerned the ball would roll out in a hunting situation. I've never had it happen 'accidently'..if you shake it inside down it will dislodge it from the cup, but there is enough friction to keep it in place for on the range.

Not sure if you can buy these anymore, I gathered them up off eBay for a few years...

What is the purpose of the raised portion on the ball?
I'm assuming it is the result of casting.
Is it filed down before use? If not, would it not affect accuracy based on spinning, etc...?
I'm not familiar with them thus just asking.
November 26th, 2021, 10:30 AM
Big Jack

Quote:

Originally Posted by impact

"There is a limit as to what an unjacketed bullet can take without stripping from the rifling, and there is also a limit as to what jacketed bullets can take as well. Anti-tank guns use sabots, as the extreme tightness of the twist that would be required to stabilize these monstrous projectiles exceeds what jackets can withstand."

"For today's muzzleloading hunter, there is no doubt that a saboted bullet can clearly outperform the bore-sized alternatives on a number of levels, and it most always does. The trajectory limitation of .50 caliber projectiles is clear, and the already loopy muzzleloading performance level is diminished dramatically by shooting larger, blunt, aerodynamically deficient projectiles."

"A .40 to .50 caliber projectile in saboted form of equal weight and style gives you a huge benefit in trajectory making good shot placement that much easier. The bullet is not chewed up or deformed by the rifling, leaving the bore in pristine condition. Out of a muzzleloader, no jacket strength is compromised. Bullets of similar style and weight not only fly flatter, they retain more of their original muzzle velocity, which enables better expansion, better penetration, or both. Penetration, expansion, and precise shot placement all translate into faster and cleaner kills."

https://www.chuckhawks.com/sabots_better_bullets.htm

This may be applicable to BP but not smokeless. And certainly if you consider your 300 win Mag or 458 win Mag they certainly don’t chew up bullets!

Sabots fail, plain and simple.

Take your 50 cal smokeless rig and pop a .458 300 grain bullet in it and top speed I personally have achieved has been a hair over 2500 FPS. Accuracy just under an inch. 100 yard good. 200 yard Ok. 300 yard bullet is not ok because sabot cannot transfer the spin to the bullet. People have tried knurled bullets to help but repeatable results aren’t there. I spent so much time and money chasing this pipe dream.

Now I take that same 458 bullet direct in rifling and at 2500 FPS it shoots 1/3 or better MOA at 300 yards.

I will outshoot your best Tikka in your cabinet because I outshoot my own.

I can also take that bullet to 3000 FPS if I want the pain associated with that.

Full bore projectiles for 50 cal are out there. Find Thor bullets. Those you can push hard.

My two cents, your mileage may vary!
November 26th, 2021, 10:31 AM
Big Jack

Quote:

Originally Posted by ET1

Big Jack

To me there are pro and cons with sabot or sabot-less. Not having shot sabot-less I can’t really give an opinion on this practice.
With sabots:
I have flexible load tolerances to play with.
I have no concerns about obturation.
I have no concerns about copper fouling.
I can put precision loads together with a sabot but also need to know what the sabot requires.

So I see no need to go sabot-less because I see no real advantage for me.

Come with me for one range session and I will change your mind.

No copper foul beyond hat you would see in a match CF barrel.

No obturation concerns

Defined repeatable accuracy is what I do get.

That is all I can say
November 26th, 2021, 01:35 PM
ET1

Big Jack
First off, I haven’t disputed anything you have said. You have found what works best with your SML as have I with using sabots. I have no intention of changing my mind nor try to change yours.
The one thing I disagree with is that sabots can transfer rotational spin which is dependent on velocity and bore twist. But this is another topic.
November 26th, 2021, 06:18 PM
Big Jack

Quote:

Originally Posted by ET1

Big Jack
First off, I haven’t disputed anything you have said. You have found what works best with your SML as have I with using sabots. I have no intention of changing my mind nor try to change yours.
The one thing I disagree with is that sabots can transfer rotational spin which is dependent on velocity and bore twist. But this is another topic.

I would be interested in hearing how you accomplish this.
How do you measure rotational spin imparted?

Couldn’t find a way myself but many claim they can!

I had mold made and a smooth form die made by Tom post. Also have a make shift die that is a piece of 10ml barrel.
Plan is to cut rifling and then smooth form to fit. The hope is holding MOA at 300
November 26th, 2021, 07:43 PM
ET1

Big Jack

No, I can’t measure rotational spin and can only see the results on target paper.
There is a formula for calculating rotational spin. Here is an example.
MV = 2800 FPS
8-Twist RPM = 2800 x (12/8) x 60 = 252,000 RPM
MV = 3200 FPS
9-Twist RPM = 3200 x (12/9) x 60 = 256,000 RPM

But what I really use is this calculator to verify if bullet is acceptable for my twist rate and velocity.
https://thebarreloutlet.com/twist-calculator/
The answer will be bore twist rate needed for flight stability

The question I have is how much rotational spin decays down range? Here’s an answer I found.
“According to a test done at the Aberdeen Proving Grounds, a bullets spin decay rate is approximately 2% per 100 yds. Bullets shed velocity at a much greater rate than spin.”

Good luck with your MOA at 300yds.
November 27th, 2021, 07:43 AM
Big Jack

Ok so that lines up to what I’m seeing to some degree. Spin is imparted but likely not at a 1:1 ratio. Hence the degraded accuracy at over 200.

I did some playing with knurling that did show some promise but repeatability was the issue.

I sometimes wonder if a grip medium between sabot and bullet would do the job
November 27th, 2021, 03:47 PM
ET1

Big Jack
Interesting comments.
First off, I don’t see rotational spin degraded at 200yds. Flight stability is good seen from groups and bullet holes. Okay I haven’t shot over 200yds but can only perceive this flight stability continues.
The only grip medium I know of is knurling bullets and good snug bore fit. If the fit is not really snug it defeats the purpose of the knurl. Another consideration is the tolerance of bullet ID after knurl. My bullets are knurled to .454” plus or minus .0005”. This is confirmed by measurement and I also run my knurled bullets through a sizing die.
https://i.postimg.cc/NjvL7gQn/Bullet-Sizing-Die.jpg

What I try to maintain with this precise method is get the same ignition/burn response between shots. Results are good.

If you should happen to find a good grip medium you have my attention.
November 27th, 2021, 06:59 PM
Big Jack

Quote:

Originally Posted by ET1

Big Jack
Interesting comments.
First off, I don’t see rotational spin degraded at 200yds. Flight stability is good seen from groups and bullet holes. Okay I haven’t shot over 200yds but can only perceive this flight stability continues.
The only grip medium I know of is knurling bullets and good snug bore fit. If the fit is not really snug it defeats the purpose of the knurl. Another consideration is the tolerance of bullet ID after knurl. My bullets are knurled to .454” plus or minus .0005”. This is confirmed by measurement and I also run my knurled bullets through a sizing die.
https://i.postimg.cc/NjvL7gQn/Bullet-Sizing-Die.jpg

What I try to maintain with this precise method is get the same ignition/burn response between shots. Results are good.

If you should happen to find a good grip medium you have my attention.

So sizing after knurling may help with repeatable results.

I was able to get sabots to 200 yards at 1.25” groups but as I said it fell apart at 300.
November 27th, 2021, 09:02 PM
ET1

Big Jack

Boy your post got me thinking. One factor I didn’t think about is what point a bullet goes transonic. This is where the shock wave at the nose of the bullet collapses.
Okay homework time.

Transonic speed occurs 1050fps at 0-F and 1160fps at 100-F
Okay let’s see what a ballistic chart reveals.
Using a 250 FTX bullet at muzzle velocity of 2300FPS

https://i.postimg.cc/SRDbPF5c/250-ba...at-2300fps.jpg

Ballistic chart shows that at 300yds you are just shy of transonic range with a muzzle velocity of 2300FPS. So, by rights rotational spin and flight stability should be maintained or so the theory goes, chuckle.

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