quote:

Originally posted by hray:
If all I plan on is shooting factory 150 grain ammo out of a Winchester M70 would there be any benefit going from standard 1/10" twist to a 1/9" or 1/8.5" twist 22" barrel?


I'm sending LRI my Win M70 sporter and having it made into a featherweight and need to select my twist rate. Thanks. Hray

quote:

Originally posted by Jim Watson:
The original 150 gr flatbase spitzer was designed for the original 10 twist. If you want to fool around with boattails and VLDs, a faster twist would pay off.

quote:

Originally posted by sigfreund:
A bullet with a boattail base will usually be longer for a certain weight, and if so, will require a faster twist to stabilize.

Although the bullet styles differ somewhat in ways besides the base design, consider two 0.308" Berger bullets. The 150 grain Target Flat Base is 1.136 inch long. The 155 grain Target Hybrid is 1.260" long, or about 11% longer despite being only 3% heavier. For “worst case” conditions the FB bullet requires a 1:12 twist rate and the Target Hybrid requires 1:10—significantly faster.

I recommend reading what Bryan Litz said about spinning a bullet faster than what’s necessary to stabilize it. If researched, his full original comments may be available online. In short, though, according to him the only advantage to a slower rifling twist rate that’s still adequate is (possibly) slightly higher precision and accuracy. There is none other unless the bullet is driven so fast and with so fast a twist that it disintegrates in flight, and that’s not going to happen with any hunting normal bullet fired from a 270 Winchester rifle.

Example: I recently tested two loads with my 223 Remington Tikka Super Varmint model that has a 1:8 rifling barrel. They were the 77 grain IMI HPBT-Match and 55 grain Frontier HP Match. Even though the 55 gr. Frontier bullet would be stabilized with a significantly slower twist rate than the 77 gr. IMI, the Frontier actually produced more precise results than the IMI; not much, but measurable. The obvious reason is that the Frontier is a better load, and it certainly didn’t suffer from being “over-stabilized” or from being spun faster than was necessary.

The same would be true of going to a flat base bullet rather than boattail: a slower rate would be what a bench rest shooter would choose, but a faster rate would not detrimental in any significant way for me.

Although it’s no sort of a recommendation either way, I choose rifling twist rates based on the length of the longest bullets I expect to fire with the rifle and with the expectation that lighter bullets will perform satisfactorily as well.

Back when I first wanted a 223 Remington Tikka rifle, the major suppliers had only models with 1:12 twist barrels. Although that would have been fine for 50-55 grain varmint hunting bullets, I wanted to be able to shoot heavier bullets as well. I finally found one with 1:8, and it shoots virtually as well as the Super Varmint I mentioned above. I am perfectly confident that both would be fine with 50 grain bullets if I went back to hunting prairie dogs, just as was my very old Ruger 77 in 22-250 with its 1:12 barrel.

As a friend first told me decades ago, we pays our money and we takes our chances, but thus far when selecting rifle barrel twist rates, my choices based on what I know about the subject have turned out well for me.