Home Forums Hunting & Shooting Ask The Gunwriters Twist rate question

Not that it matters, was thinking about it while reading the velocity/pressure thread. Was always curious how steep of a twist rate before a bullet would plow over the lands rather than spin with them. Read somewhere, perhaps an old Precision Shooting Magazine, not sure. They were playing with barrels twisted with increasingly steep twist rates until they reached a twist rate of 1-4 or 1-3? where bullets would not grab the lands and rotate but rather simply plowed over the lands, developing instant overpressure when bullet meets lands, bullet would tear/strip/fragment on its travel down the bore. Anybody have any insite?

Lot of variables there, but pistol reloaders deal with this all the time. And who knows how many swear words have been said on polygonal barrels, Glocks, and soft lead reloads.

This may be where a “gain twist” (rifle starts with slower twist and increases farther down the barrel) rifle would benefit. S&W does that with the 460 XVR ! memtb

BuffordBoone here has a 4 twist, 30 cal barrel and experiences bullet poofs (scientific term) at normal velocities. ...been meaning to ping him to weigh in on the pressure thread. ...now I can ask him about weighing in here as well.

I personally wondered how rifling plowing a new furrow constantly as I imagine is happening with a gain twist barrel leads to less pressure.

I agree that there are too many variables at play to simply put a number on it. The translational acceleration would have to exceed angular acceleration, with additional dependency on the force required to displace bullet material over time, all of which depends on the rifling geometry and style, bullet jacket material, bore and groove dimensions, etc. Even if it were to happen, the bullet would start rotating along it’s path down the barrel as translational acceleration begins to decrease, likely before the rifling completes a full rotation.

Disintegration after the bullet exits the barrel is typically caused by over-rotation, in which the centrifugal (pseudo)force exceeds the centripetal force exerted by the interatomic bonds that hold the bullet together. Though, the rifling smearing the jacket certainly wouldn’t help.

I have witnessed two guns/loads exceed the integrity of a bullet. One was a Savage target model 22-250 1:9 with 40 gr Hornadys that stated for use in the Hornet. It would make it about ten to fifteen feet and just turn to a gray dust. The other was my 300Bee 1:10 with 110 gr round noses for M1 carbine. I loaded too much 7828 when a breeze turned the page on my manual and used 180 gr data with 220 gr Sierras. So I pulled the heavies and just stuffed the RN on top. They made it to the target, but disintegrated from the paper/cardboard target.

I would really like to have tried it on a squirrel!

Why would anyone load bullets in a windy place? I can think of a lot of things that can go bad. miles

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I've seen fast twist (1:4 .308) spin lightly constructed (SMK) bullets apart right in front of the muzzle when loaded to traditional velocity. That same barrel has also shown better (Higher) BC and more consistent BC when those bullets were launched at about 1700 if compared to the same MV from a 1:7 twist.

More robust bullets (Bonded or solid copper) stayed intact and enjoyed shorter time of flight than when fired from a traditional twist rate barrel.

I've been present when a 1:1 barrel was tested on radar. It was a 8.6 Blackout. Not only did the bullets survive, they showed no indication of "plowing over the lands". Interestingly enough, the radar data was worse than the 1:3 barrel we shot just before it. We know what the bullets looked like as we ran high speed video for that very purpose.

Someone remarked "I believe we've gone a twist too far".

Because kids took up every room in the house. So garage bench it was, for years. That's the only load I ever popped a primer and had to pull bullets.

It was windy in your garage? Maybe shut the door. miles

I said a breeze, not windy. JFC.

Seems to have turned your page and made a bad load. I call that windy, or careless. miles

Hence why guys who load outside at the range or at the shooting bench when there is no reloading building use powder throwers to tune their load.