I was e-mailing a customer in the U.K. who had some questions large increases in twist rate. So, I thought I'd share.
We have done a few barrels with a large increase in twist. From the reports we received, they shoot fine. However, I generally do not recommend it. We have found that there is no statistically significant reduction in pressure or increase in velocity with the gain twist barrels (They won't be slower than a straight twist barrel, but any gains likely represent nominal differences that exist from barrel to barrel). The main benefit of the gain twist appears to be a reduction in vibration and harmonics. With the gain twist, the bullet is always under constant resistance from the increasing twist rate. This resistance acts like a mechanically choke and provides a better gas seal. This resistance also seems to extend the pressure curve out further, keeping the barrel stretched forward, reducing vibration and limiting the harmonic effects. This reduction in vibration can provide better accuracy. By keeping the amount of increase in twist rate relatively small, the amount of distortion to the bullet jacket is kept at a minimum. In a large increase in twist, the amount of distortion to the jacket could be detrimental to accuracy and increase the possibility of jacket failure. At this point in time, we have found the best result using .75 – 1.00 inch increase in twist rate, depending of barrel length. Some shooters have even been experimenting with an increase as small as .10 of an inch on a 22 inch barrel (the results are interesting, but not enough data has been gathered for a conclusion yet).
We have done a few barrels with a large increase in twist. From the reports we received, they shoot fine. However, I generally do not recommend it. We have found that there is no statistically significant reduction in pressure or increase in velocity with the gain twist barrels (They won't be slower than a straight twist barrel, but any gains likely represent nominal differences that exist from barrel to barrel). The main benefit of the gain twist appears to be a reduction in vibration and harmonics. With the gain twist, the bullet is always under constant resistance from the increasing twist rate. This resistance acts like a mechanically choke and provides a better gas seal. This resistance also seems to extend the pressure curve out further, keeping the barrel stretched forward, reducing vibration and limiting the harmonic effects. This reduction in vibration can provide better accuracy. By keeping the amount of increase in twist rate relatively small, the amount of distortion to the bullet jacket is kept at a minimum. In a large increase in twist, the amount of distortion to the jacket could be detrimental to accuracy and increase the possibility of jacket failure. At this point in time, we have found the best result using .75 – 1.00 inch increase in twist rate, depending of barrel length. Some shooters have even been experimenting with an increase as small as .10 of an inch on a 22 inch barrel (the results are interesting, but not enough data has been gathered for a conclusion yet).