Does twist rate affect pressure?

longcummins · December 2, 2015, 06:31 PM

So as the title ask how much does the twist rate change pressure on a given round. Lets say going from a 1 in 10 twist to a 1 in 7 in a typical ar-15 5.56. This is something I have been curious about for quite some time. Thanks for any information or experience that you can or will share.

Nick_C_S · December 2, 2015, 07:15 PM

I don't know.

But . . .

Logic tells me that a higher twist rate will increase the bullet's "reluctance" to travel down the barrel. A corresponding increase in pressure would result.

Like you, I'll be waiting for someone more educated than me on the subject to chime in.

longcummins · December 2, 2015, 07:49 PM

Logic tells me the same, but my curious side ask how much it does change.

SHR970 · December 2, 2015, 08:59 PM

Twist rate change is ONE of the variables in pressure. Odd or Even lands and grooves? Smoothness of bore? Loose or tight tolerance bore? Freebore
? Etc.

TXAZ · December 2, 2015, 09:31 PM

It does. Since it takes energy to spin a ~ cylinder at 100K RPM, then that energy has to come from somewhere. That spin energy will slow the bullet down, increasing the pressure. If if didn't then that energy would go into pushing the bullet faster down the barrel.

How much energy, and the resulting pressure delta, is left as an exercise to the reader

December 2, 2015, 06:31 PM	#1
longcummins Junior Member Join Date: March 7, 2015 Posts: 6	Does twist rate affect pressure? So as the title ask how much does the twist rate change pressure on a given round. Lets say going from a 1 in 10 twist to a 1 in 7 in a typical ar-15 5.56. This is something I have been curious about for quite some time. Thanks for any information or experience that you can or will share.

December 2, 2015, 07:15 PM	#2
Nick_C_S Senior Member Join Date: March 21, 2013 Location: Idaho Posts: 5,522	I don't know. But . . . Logic tells me that a higher twist rate will increase the bullet's "reluctance" to travel down the barrel. A corresponding increase in pressure would result. Like you, I'll be waiting for someone more educated than me on the subject to chime in. __________________ Gun control laws benefit only criminals and politicians - but then, I repeat myself. Life Member, National Rifle Association

December 2, 2015, 09:31 PM	#5
TXAZ Senior Member Join Date: September 5, 2010 Location: McMurdo Sound Texas Posts: 4,322	It does. Since it takes energy to spin a ~ cylinder at 100K RPM, then that energy has to come from somewhere. That spin energy will slow the bullet down, increasing the pressure. If if didn't then that energy would go into pushing the bullet faster down the barrel. How much energy, and the resulting pressure delta, is left as an exercise to the reader __________________ Cave illos in guns et backhoes Last edited by TXAZ; December 2, 2015 at 10:14 PM.

December 2, 2015, 07:49 PM	#3
longcummins Junior Member Join Date: March 7, 2015 Posts: 6	Logic tells me the same, but my curious side ask how much it does change.

December 2, 2015, 08:59 PM	#4
SHR970 Senior Member Join Date: January 24, 2011 Posts: 1,427	Twist rate change is ONE of the variables in pressure. Odd or Even lands and grooves? Smoothness of bore? Loose or tight tolerance bore? Freebore ? Etc.