Berger Jacket Limitations with Velocity?

[Huntnful]

So I was out shooting LR with my buddy the other day. He was shooting a 6.5 STW pushing a 156 EOL at 3400fps with great accuracy. It was very intriguing to say the least. 16.5 MOA @ 1000 yards. It got me wondering, how fast can you really push them? And does the thinner jacket of the hunting bullet effect the maximum speed. Has anyone pushed a berger to the jacket failure limit? What were you velocities? And do you need to over twist the bullets to stabilize them at these speeds?

I'm shooting a .28 nos throated for the 195's with 1-8 twist. I push them at 3030fps pretty easy with N570. Now I'm curious about like a 175 @3300 or so. Just my brain churning a little bit. Curious to hear from people who have tinkered with this!!

 

[brant89]

I've not personally experienced this, but I saw a number that was reported as coming directly from Berger stating that the J4 jackets on their .224 90gr VLD could only withstand approximately 300,000 rpm and a similar number was quoted by Hornady for the 88gr ELD. Reports of jacket separation with these bullets in 22BR and 22-250 seems to support this. I don't know that any of this would carry over to other calibers.

 

[Huntnful]

I've not personally experienced this, but I saw a number that was reported as coming directly from Berger stating that the J4 jackets on their .224 90gr VLD could only withstand approximately 300,000 rpm and a similar number was quoted by Hornady for the 88gr ELD. Reports of jacket separation with these bullets in 22BR and 22-250 seems to support this. I don't know that any of this would carry over to other calibers.

Pardon my ignorance. But how do you transition velocity and barrel twist into RPMs?

 

[brant89]

(Muzzle Velocity / Twist Rate) X 720 = Bullet RPM

(3000fps / 7tw) X 720 = 308,571 rpm

 

[Huntnful]

Very cool! Thanks dude!

 

[MagnumManiac]

I heard the same limitation of 300,000rpm was the max.
I keep hearing about Hornady 6.5 bullets tearing themselves apart, but haven't witnessed it personally.
I have blown up 30 cal 125gr TNT pills from a 300WM pushing them to 3500fps.
They would only make it 15-20 yards from the muzzle then you would see a bluish puff and a streak in the air. Never saw anything on a 100y target but did at 50y and was peppered with tiny shrapnel.

Cheers.

 

[brant89]

It seems like the simple solution would be a slower twist, but once you start digging into the numbers you realize that higher velocities require higher rpm to fully stabilize, and sacrificing stability factor can result in reduced BC. So basically, yes, it appears as though there is an upper velocity limit for these long bullets with very thin jackets. You can't eat your cake and have it too...

 

[DJ Fergus]

So I was out shooting LR with my buddy the other day. He was shooting a 6.5 STW pushing a 156 EOL at 3400fps with great accuracy. It was very intriguing to say the least. 16.5 MOA @ 1000 yards. It got me wondering, how fast can you really push them? And does the thinner jacket of the hunting bullet effect the maximum speed. Has anyone pushed a berger to the jacket failure limit? What were you velocities? And do you need to over twist the bullets to stabilize them at these speeds?

I'm shooting a .28 nos throated for the 195's with 1-8 twist. I push them at 3030fps pretty easy with N570. Now I'm curious about like a 175 @3300 or so. Just my brain churning a little bit. Curious to hear from people who have tinkered with this!!

The land & groove configuration along with the condition of the bore will have a significant impact on whether the jacket gets slung off or not. 5R & 6 groove barrels are less likely to sling jackets off at higher velocities. I've pushed 88 elds to 3350 fps in a 7 twist 6 groove repeatedly with no issues.

 

[brant89]

The land & groove configuration along with the condition of the bore will have a significant impact on whether the jacket gets slung off or not. 5R & 6 groove barrels are less likely to sling jackets off at higher velocities. I've pushed 88 elds to 3350 fps in a 7 twist 6 groove repeatedly with no issues.

I've seen some reports on this as well. I guess I should add to my comment that there are other factors that can affect what that MAX rpm number is.

 

[L.Sherm]

It seems like the simple solution would be a slower twist, but once you start digging into the numbers you realize that higher velocities require higher rpm to fully stabilize, and sacrificing stability factor can result in reduced BC

How come when you run the numbers on a certain twist - bullet combo and increase the velocity the S.G and stability factor goes up

 

[Rardoin]

@DJ Fergus hit upon a very important factor....bore condition. If the throat is really firecracked and it extends a bit past the throat it will cause an increase in likelihood of jacket failure even at less than excessive velocity. A 'straight' cut groove that engraves the bullet closer to a right angle will put more stress on the jacket than a canted land or radiused land bore. Shallower grooves and uneven groove number also seem to produce less jacket failures. One must consider all of these factors in addition to velocity and twist rate when looking for jacket failure cause. I had a 6.5 x55 BJAI that loved a custom 142gr bullet at 2940fps (Precision Ballistics made with J4 jackets). Not smoking velocity by any stretch. I had used several Bartlein 5R 8tw barrels over 2 years of competition then switched to a Brux 4 groove 7.5tw to test Sierra 150's. I switched back to the 142 PB's after finding no joy with the 150 SMK's. At about 900rds I lost 2 of the 142 PB's in a match; they went 'poof' about 150yds downrange. The throat was fairly firecracked for about 3" past the start of the lead but nothing that the 5R barrels did not handle up to 1800rds of life (without ever shredding a bullet). After discussion with a barrel maker it appears that the perfect storm was the even numbered/straight cut rifling, the roughness of the throat/initial bore and the extra RPM of the 7.5twist was too much for the jacket to handle.

 

[264MHC]

Assuming you stick to the 300,000 RPM theoretical limit, an 8 Twist is good for up to 3333 FPS regardless of bullet so a 175 at 3300 in your 8 twist should be fine and will absolutely be fully stable in all conditions, as long as it's above -70 F at sea level haha. Assuming your buddy's STW is an 8 twist, he is probably pushing it at 3400 but I'm sure there's a little leeway both directions where the factors (bore/throat condition, land number/type) others have mentioned come into play.

 

[brant89]

How come when you run the numbers on a certain twist - bullet combo and increase the velocity the S.G and stability factor goes up

Because the rpm's are going up with the velocity. If you increase the velocity but reduce the twist rate so that the rpms stay the same, the stability will go down. For example, if you push a 88eld 2912fps from a 7 twist you get 300,000rpm and a SF of 1.759. If you go with an 8 twist to stay below that 300,000rpm number you can push it 3333fps, but your SF is only 1.409.

 

[L.Sherm]

higher velocities require higher rpm

I guess I'm not getting the jest of why higher velocity require higher rpm.
You can have higher velocity and slow down the rpm's with slower twist.