Gain Twist

[Throwback]

A quick query for any historians out there... Has anyone embarked on any meaningful tests of gain twist in smallbore rifles (.30 or less) with the goal of achieving something like jacketed bullet velocity without the yaw associated with a boolit torqued beyond its design and composition envelope?

[Wayne Smith]

No, but if you can find an original, uncut Circano you will get to try. If I remember right Pope believed in the gain twist.

[SvenLindquist]

I know my 450 BM AR had a gain twist and would not shoot boolits very well whereas my Ruger American has a fixed twist and loves boolits.

[waksupi]

Harry Pope and the other old timers played with gain twist a lot. They didn't reach a conclusion that it was any better than straight cut rifling. They were mostly shooting .36-.38 bore size generally, and weren't going for the velocity you are seeking though. They were interested in accuracy before anything else.

[ukrifleman]

237171237172237173The Italians developed gain twist rifling mainly to cut down on bore wear.

Gain twist bores are not the easiest to load cast for, but it can be done.

My Mod 1891 Carcano shoots well enough for a military rifle with a cut down Lee Cruise Missile (150gn)

ukrifleman

[country gent]

There are very few cutting gain twist barrels any more. On the sine bar rifling machines the normal rifling is a straight edge the follower rides along. For gain twist the bar is a parabolic edge the follower follows. the angle sets the twist the parabolic radius the increase rate. Its a much trickier set up and tooling. I think the 20mm use a gain twist barrel tough.

[Johnch]

I have a 7 x 57 Mauser with Gain twist
I have played with cast in it .... but I was working on a 160 gr cast bullet at 1600 - 1800 FPS

Some loads shot great
Other loads the groups were 12 - 16" at 100 yards

I found in my rifle at least , I needed to work to find a great shooting load
But 2 - 3" loads common to get

John

[MT Chambers]

Ron Smith of Alberta Canada produces gain twist barrels that are much sought after by shuetzen shooters, with a long waiting list.

[BCB]

I never understood how that type of twist could work at all…

Once the boolit/bullet engraves with initial contact the riflings have a specific turn…

Then as the twist changes, I would figure it would alter the original engraving and widen the original starting engraving, making for some type of loose fit or wobble…

I didn’t explain myself well, but I don’t understand the rifling change engravement (I just made that word up!)…

Good-luck…BCB

[DonMountain]

I never understood how that type of twist could work at all…

Once the boolit/bullet engraves with initial contact the riflings have a specific turn…

Then as the twist changes, I would figure it would alter the original engraving and widen the original starting engraving, making for some type of loose fit or wobble…

This is probably why gain-twist rifling has never produced any followers. That plus the difficulty in cutting it. Since a bullet, when fired from the cartridge, especially in a rifle with slow burning powders, accelerates both in straight line velocity and rotational speed. Since rotational velocity is always proportional to straight line velocity with straight cut rifling. So attempting to spin up the bullet in rotational velocity faster than the straight line velocity has proven to be not a good solution. And at the least would require a hard, jacketed bullet to minimize tumbling from the stripped bullet.

[MT Chambers]

The advantage is with soft cast boolits, usually breech seated, smokeless or black, 1200-1400fps. The great results are out there, prolly barrels are difficult to make in this style.

[Mal Paso]

Smith & Wesson advertised gain twist rifling in the XVR 460 revolver but I see no mention now on their web site.

[Green Frog]

Gain twist rifling is much too complex a topic for an inter-web thread... there is a LOT of history out there. As others have said, in the halcyon days of Schetzen competitions, some of the best builders and shooters used it to get the absolute best accuracy available... for lead bullets from rifles at black powder velocities. As that sport was supplanted by the use of military rifles and jacketed bullets, the market for and use of the gain twist system dried up. There was nothing wrong with the system (rather than expense and difficulty of building) but it became obsolete with regard to the type of shooting that became prevalent. Anyone interested in more information about gain twist can go over to ASSRA.com and poke around a bit. There are also many books available about the sport of Schuetzen if one looks for them.

Froggie

[fourarmed]

Some are being made for long range use in the AR. They allow higher velocity with long heavy bullets without raising pressure. IIRC, they start out at about 12" or 14", and wind up around 6" at the muzzle.