Everything else being equal, does twist rate impact pressure?


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duck911
December 12, 2010, 07:04 PM
Well, that's the question!

If the same .223 rifle shoots the same load and everything else is theoretically the same except the twist, will a 1-9" twist create the same pressure as a 1-12" twist?

thanks!

--Duck911

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Black Butte
December 12, 2010, 07:14 PM
No, a 1-in-9 inch twist will not have the same pressure curve as a 1-in-12 inch twist with all other variables held equal. Pressures increase as the twist tightens. There is a lag time with tighter twists because more work is required to move the bullet down the barrel because of the increase rotational kinetic energy as the bullet follows the rifling, therefore, the pressure from the burning powder has more time to build up behind the bullet as it propelled down the barrel.

Greg Mercurio
December 12, 2010, 09:44 PM
No.

Walkalong
December 12, 2010, 09:51 PM
Sure it will, but not enough to worry about. If you are following good load data, you will not have a problem.

243winxb
December 13, 2010, 08:17 AM
Everything else being equal, does twist rate impact pressure?
Yes will a 1-9" twist create the same pressure as a 1-12" twist?

No. Your title and question are confusing. http://castboolits.gunloads.com/images/smilies/killpc.gif

JimKirk
December 13, 2010, 08:53 AM
Anytime you increase the twist rate, all else being the equal, pressures will increase. Will the increase be a problem, not unless you are on the edge of maximum pressure already.

Jimmy K

ranger335v
December 13, 2010, 12:36 PM
In theory, sure. But, in fact, so little as to be irrelivant. And that little only for the time it takes for the bullet's bearing surface to travel a small part of it's total length...a couple of nano-seconds maybe?

918v
December 13, 2010, 01:00 PM
In some guns, like the older TC Contenders, the pressure created by 1-9" may be too much. Bullberry wouldn't make me a fast twist barrel saying it would spring the frame. The newer Contenders are much stronger, though.

Walkalong
December 13, 2010, 01:55 PM
Are they saying the torque will spring the frame then?

Clark
December 13, 2010, 05:15 PM
I could calculate the change in pressure, but with .223, why bother?

The 223 is registered at 55,000 psi.
The load books max load is much less.
The 223 brass and guns are happy at 75,000 psi.

The little bit added by twist will not matter.

If you want to ask about 270, where is is registered at 65,000 psi, the old books have real loads, and the brass is only good for 70,000 psi, then maybe, just maybe, we could concern ourselves.

CraigC
December 13, 2010, 05:50 PM
Yes. I know that in sixguns, John Linebaugh uses a slower twist for his five-shot .45Colt's than Ruger because it does in fact decrease pressure slightly. Although they use heavier bullets, the increased velocity means that you do not need near as fast a twist rate to stabilize the bullet. Which is why the twist rate of the .454 is 1-24", while the .45Colt is 1-16".

GaryL
December 13, 2010, 09:47 PM
I think with the 45 colt, it's much like putting spin on a bowling ball - a little doesn't hurt, a lot won't matter.

918v
December 14, 2010, 02:19 AM
Are they saying the torque will spring the frame then?


No, they said it created additional backthrust and they had broken several frames that way.

CraigC
December 14, 2010, 11:44 AM
I think with the 45 colt, it's much like putting spin on a bowling ball - a little doesn't hurt, a lot won't matter.
Apparently it matters enough for Linebaugh to replace a Ruger 1-16" barrel with a 1-20". We're not talking 14,000psi cowboy loads but 50-55,000psi.

rbernie
December 14, 2010, 05:02 PM
As an aside, many of the 6.8 SPC barrel makers have both adopted the SPCII chamber spec and also moved from a 1:9.5" or 1:10" twist to a 1:11" twist as a means of reducing peak pressures. Nobody has been able to quantify (at least that I've seen) the actual pressure curve differences attributable to the change in twist rate, but SOMEBODY has been convinced that it's a valid issue.

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