Gain twist rifling

mtnclimber · Jul 22, 2014

Has anyone had any experience with this type of rifling? Gain twist, progressive twist, transitional rifling, whatever you wanna call it. An example would be .338 cal starting at 1:14 at the breech and end with a 1:7 at the muzzle. It almost sounds like defensive edges +P they do, obviously much different but attempting to achieve the same end result. Lower pressure, higher FPS.

Whadda ya think?

Shrek · Jul 22, 2014

I've read a few articles over the years and some of the very best barrel makers have tried it and some still do it but they all seem to say it's very hard to make work and very even regular rifling works better for them. Dan Lilja comes to mind right off and obermeyer I think. I think that Lilja's take on a bore being too smooth is right also. A fine "scratch" going with the direction of travel reduces friction and fouling.

rayporter · Jul 22, 2014

i can't speak for a 338 but a 6mm will do very well if you go to something like a 14 to maybe a 13.8 or 13.5 twist. it is very accurate and you might say the best thing going.

i have not talked to anyone that tried that much gain.

Shrek · Jul 22, 2014

As I understand it you can't get away with much gain without tearing the jacket apart. I can't remember exactly right now but I think it was less that 1 twist.

HellsCanyon · Jul 22, 2014

Haven't tried it. Wanted to! From what I've researched it doesn't sound like it can hurt as long as you stay close to the optimal twist rate for the caliber and weight bullet you're wanting to shoot. My theory is it works best on chambers where you have a lot of powder room. Like the 338 Edge, or any of the RUMS and it should be used on the bigger bullets meaning I doubt you'd see any benefits on a 160 grain 7mm bullet out of a 7RUM case but that's just my theory.

Been tempted to try a 338 Norma with a 28" barrel going from a 1:12-1:9" twist to see what it would do. But that chamber has been so accurate out of a standard 1:9" twist that the saying "if it ain't broke don't fix it" comes to mind.

I've talked with a few barrel makers and none of them have said it's better though a few have offered to do it.

Mike

Shrek · Jul 22, 2014

What I took from all the study I did was that if you get the twist rate extremely even over the length of the barrel and get the bore surface the right texture that that will be the best. The gain twist was more to mask variations in twist and that the constant cutting of new jacket adds drag and slows the bullet. A very even twist and lands will cut and then ride with much less drag and the even rifling doesn't wallow out the grooves cut in the bullet and let gas escape.

Shrek · Jul 22, 2014

Mike , what's your take on a barrel being too smooth and making it sticky.

HellsCanyon · Jul 22, 2014

Shrek said:
Mike , what's your take on a barrel being too smooth and making it sticky.

I know we've seen velocities INCREASE after being shot 50-100 rounds on some barrels. Could be a few things but from my experience I would say it's because the copper jackets over X amount of rounds fired smoothes out the rifling and fills in the tiny imperfections. This is a big reason why we don't clean for copper but every 250-500 rounds depending on chamber. And when I do copper clean I only use patches no brushes. Rifle "settles back in" much better when only using patches. 3-6 shots and she's back with a very consistent zero compared to 10-14 shots if I used brushes.

The gain twist can be done very accurately with cut rifled barrels. Even a static twist button rifled barrel will have some variations in twist time to time depending on manufacturer and quality of steel being used as well as how much force is required to pull that button through the barrel.

Mike

wapitibob · Jul 23, 2014

I might have to try leaving the copper in mine. I clean copper after 100 or so and only get a little bit. I have 10 rounds laying on the bench ready for fowling before season opens In a cpl weeks. Are you just running some butches or similar thru it?

JustOneMoreShot · Jul 23, 2014

https://www.youtube.com/watch?v=sBkrg7JMGdw
Snipers Hide is a very good resource for tactical shooting. The members on the board are mostly no BS and can be a little gruff so be prepared and have thick skin. The owner is Frank and he has a gain twist barrel on his .300 Norma Mag. He shoots a very specific and particular bullet thru it exclusively and the barrel and bullet were specd for each other.
It is a Bartlein barrel that he is running and there is a video that SH shot recently at the factory and they talk a little about the gain twist rifling. You can search more on SnipersHide if you wanted more info on gain twist. There is plenty over there.
I hope this helps you get started.

HellsCanyon · Jul 23, 2014

Those monolithic bullets he's shooting are stupid expensive. Each one hand turned on a lathe to precise measurements.... I don't think I'd ever have the patience for that. I like pulling the trigger way too much to spend that much time/money on each trigger pull

30338 · Jul 23, 2014

My Rock 7mm barrel is an 8.5 twist. They use a gain twist method and I don't know if it starts out at 9 and finishes at 8.5 or starts at 8.5 and finishes at 8 or so. It does shoot quite well though.

Gain twist rifling

mtnclimber

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Shrek

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rayporter

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Shrek

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HellsCanyon

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Shrek

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Shrek

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HellsCanyon

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wapitibob

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JustOneMoreShot

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HellsCanyon

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30338

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