TWIST: Difference in handgun vs. rifle for same caliber

TXAZ · July 13, 2013, 11:14 AM

Question for you twist wizards: If you had a pistol, using a specific bullet & cartridge, then wanted a rifle using the same bullet & cartridge, would you need or want a different twist for the rifle vs. the pistol?

Assume the rifle is used for much longer range shooting.

If not, why not?

Thanks!

JD0x0 · July 13, 2013, 01:46 PM

Depends on bullet length (weight)

Increased barrel length tends to increase velocity. A bullet moving faster through the barrel will be spinning faster, so theoretically you could have a slower twist in the rifle and achieve the same spin rate. Tighter twists tend to cause more friction but I'm sure it's fairly negligible.

You wont "need" a different twist for a longer barrel. It's possible to need a faster twist for a shorter barrel if the bullet isn't pushed fasted enough, it may not be spun fast enough and therefore can be unstable.

For the most part, most pistol and revolver cartridges can share twist rates between the pistols and rifles. Generally the pistol twist rate is fast enough, so if it's stabile in the pistol it will be stabile in a rifle, and the rifle wont "over spin" the bullets.

One thing I should clear up, is that a longer barrel wont stabilize a bullet better simply because it's longer. I've had people claim that the bullet doesn't "catch" the rifling right away, so a short barrel may not stabilize the bullet. That is simply not true. If your bullets aren't "catching" the rifling right away your bullets are undersized or your bore is oversized, and it likely wont catch any better down the barrel. You get more stability with a longer barrel because the bullets generally exit faster. If a bullet is moving through a given twist rate, the faster it moves through the rifling, the faster it spins.
If two identical bullets leave two different barrels, one 3'' and one 28'' with equal twist rates, and the bullets leave the barrel at the same velocity, they both should have equal spin rates, and therefore the same stability.

James K · July 13, 2013, 09:21 PM

The main factor in determining rifling twist is not the barrel length but the bullet length and the ratio of diameter to length. A longer bullet (like most rifle bullets) will require more twist for stability. Most handgun bullets are pretty short (imagine a .30 caliber 220 grain bullet in a .32 ACP case!!) so require a slower twist.

For rifles like the .30-'06 which is loaded with a wide variety of bullets, manufacturers choose a compromise twist rate (usually 1:10) which will be OK for the medium bullet range (150-180 grain) but perhaps not so good at the extremes (110-220 grain).

Jim

Jim Watson · July 13, 2013, 09:43 PM

The only time that situation would occur would be with something like a Contender or XP100 in what is really a rifle caliber to begin with, OR something like a lever action carbine shooting what is really a pistol caliber.

Theoretically, the shorter barrel should have a faster twist because it will develop less velocity and consequently slower rotation. But the effect is small in most cases.

July 13, 2013, 11:14 AM	#1
TXAZ Senior Member Join Date: September 5, 2010 Location: McMurdo Sound Texas Posts: 4,322	TWIST: Difference in handgun vs. rifle for same caliber Question for you twist wizards: If you had a pistol, using a specific bullet & cartridge, then wanted a rifle using the same bullet & cartridge, would you need or want a different twist for the rifle vs. the pistol? Assume the rifle is used for much longer range shooting. If not, why not? Thanks! __________________ Cave illos in guns et backhoes

July 13, 2013, 01:46 PM	#2
JD0x0 Senior Member Join Date: January 30, 2013 Posts: 1,037	Depends on bullet length (weight) Increased barrel length tends to increase velocity. A bullet moving faster through the barrel will be spinning faster, so theoretically you could have a slower twist in the rifle and achieve the same spin rate. Tighter twists tend to cause more friction but I'm sure it's fairly negligible. You wont "need" a different twist for a longer barrel. It's possible to need a faster twist for a shorter barrel if the bullet isn't pushed fasted enough, it may not be spun fast enough and therefore can be unstable. For the most part, most pistol and revolver cartridges can share twist rates between the pistols and rifles. Generally the pistol twist rate is fast enough, so if it's stabile in the pistol it will be stabile in a rifle, and the rifle wont "over spin" the bullets. One thing I should clear up, is that a longer barrel wont stabilize a bullet better simply because it's longer. I've had people claim that the bullet doesn't "catch" the rifling right away, so a short barrel may not stabilize the bullet. That is simply not true. If your bullets aren't "catching" the rifling right away your bullets are undersized or your bore is oversized, and it likely wont catch any better down the barrel. You get more stability with a longer barrel because the bullets generally exit faster. If a bullet is moving through a given twist rate, the faster it moves through the rifling, the faster it spins. If two identical bullets leave two different barrels, one 3'' and one 28'' with equal twist rates, and the bullets leave the barrel at the same velocity, they both should have equal spin rates, and therefore the same stability. Last edited by JD0x0; July 13, 2013 at 01:53 PM.

July 13, 2013, 09:21 PM	#3
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	The main factor in determining rifling twist is not the barrel length but the bullet length and the ratio of diameter to length. A longer bullet (like most rifle bullets) will require more twist for stability. Most handgun bullets are pretty short (imagine a .30 caliber 220 grain bullet in a .32 ACP case!!) so require a slower twist. For rifles like the .30-'06 which is loaded with a wide variety of bullets, manufacturers choose a compromise twist rate (usually 1:10) which will be OK for the medium bullet range (150-180 grain) but perhaps not so good at the extremes (110-220 grain). Jim

July 13, 2013, 09:43 PM	#4
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,543	The only time that situation would occur would be with something like a Contender or XP100 in what is really a rifle caliber to begin with, OR something like a lever action carbine shooting what is really a pistol caliber. Theoretically, the shorter barrel should have a faster twist because it will develop less velocity and consequently slower rotation. But the effect is small in most cases.