I am wondering if there is such a thing as 'too fast of a twist' for a bullet? I read a line on bergers website to the affect of "use the slowest recommended twist"
for example, let's say I want to shoot a 160gr bullet for whitetails and Berger recommends a 1:11. Then in the same caliber I want to shoot a 230gr for elk, which using the same calculator might recommend a 1:9.
Would I be spinning the 160 too fast in the 9 twist, causing stability issues? Or would I be better off splitting the difference and getting a 10 twist barrel?
Not sure if there is a general rule of them for this or not (using bergers stability calculator it appeared both examples would stabilize in the 9, but I wasn't sure what exactly it was...or was not factoring in the equation)
thank you in advance for any feedback. Scott
I do believe that you can go with a twist rate that is to fast for many reasons. here are some examples.
Extremely high velocity can cause bullet problems with fast twist barrels because of the inertia of the bullet not wanting to rotate causing engraving issues and in extreme cases jacket separation from the core. The heavier the bullet is at the same velocity, the worse the problem.
The number of groves also has a bearing on this. Most dangerous game rifles shooting 400+ grain bullets work best with 8 grove barrels with a slower twist rate.
Pistols that shoot heavy bullets, even though they are slow, have slow twist rates because of the thinner jackets on pistol bullets.
When the AR 15 became a favorite match rifle, bigger, heavier bullets were needed for the 600+ yard matches and some tried the 1 in 6 twist for the largest bullets thinking it would be better than a 1 in 7 or a 1 in 8 twist, most have replaced there barrels with the 1 In 7 or gone back to the 1 in 8 for overall performance.
My best personal example of this was with a 31" barreled 7 STW. I purposely made it with a long barrel to squeeze every bit of velocity out of it. I had very good results with a 7 Rem Mag for 1000+ yard matches with a 168 grain Match King in a 1 in 9,3 twist at 3254 ft/sec velocity, so i barreled the STW with a 1 in 9 thinking I might want to shoot the 175s. I started testing with 140 gr bullets to see what velocity I could achieve in the STW.
The rifle performed well until I went over 3750 ft/sec and accuracy went away. puzzled, I tried to shoot at 50Yards to see if I could come up with a reason for the problem, and there it was. The first shot at 50 yards showed two separate holes (One was the core, and one was the jacket) The fast twist was sheering the jackets of in the barrel at these velocities. I also tried a monolithic solid and when I recovered the bullets, the engraving was far from clean. By this time the rifle had several hundred rounds through it and upon close examination of the engraving in the bullet and the lands of the rifling, the edges of the rifling were no longer sharp on the turning/loading side of the lands. after reducing the velocity to 3500 ft/sec accuracy was just not there anymore with the original test loads that shot well.
So it appears that the bench rest philosophy of slower is better may have a lot of merit. barrel life may be better and bullet engraving is definitely better with the slower twist rates. The length of the bullet body can also have an effect on twist rates One of the reasons the Berger like the slower twist rate, is because with the Secant Ojive and the Boat tail the bullet body is very short placing more load on the surface of the bullet body. you might also try a flat base bullet with a long body to see if this solves your problem. (The Nosler partition is an example of this type of bullet).
I generally chose a twist rate that will shoot all bullet weights within reason and seldom go with the fastest twist the barrel makers offer. And I never choose one that is recommended for "ONE" bullet because if the rifle doesn't like that bullet you are stuck.
Knowing the best twist rate for your needs is very important and staying within boundaries can be difficult, so choose wisely .
J E CUSTOM
