gain twist rifle

[Heavy lead]

I have a question on gain twist rifleing. I understand the new smith 460 has gain twist rifleing. I understand the concept, but I can't wrap my brain around something. When you shoot a bullet out of a regular rifled barrel the bore will be pressed into the bullet at an angle of the twist. This would be consistant down the length of the barrel. It seems to me with gain twist rifleing the bullet (whether lead or jacketed) would tear or have to reswage as the rifle twist increased?
Any experience or thoughts?

[DLCTEX]

Same thought I had when I read about the gain twist. DALE

[MakeMineA10mm]

Well, I think the THEORY is that the boolit's sides are already engraved and engaged by the rifling, so as it speeds into the faster twist end of things, that engagement merely spins the boolit at higher RPM.

Now, in practice, I'm not so sure, and I have a similar concern to yours. That boolit is going awfully fast down the barrel, and the depth of the rifling is not that deep in the grand scheme of things. At 460 velocities, it makes me worry about what you describe (which I call "slippage") or even the boolit outright stripping out of the rifling. I think gain-twist works much better with lower-velocity rounds.

The rifling I like best is some incarnation of the Obermyer R5 rifling. This rifling is not gain twist, rather it is a profile where the sides of the lands go down towards the valley of the grooves at a tapered angle or slope, so that there is not a deep 90-degree corner at the intersection of the land and groove. I think this makes a lot of sense, because it decreases the stresses needed for the bullet to completely obturate. I have serious doubts bullets really truly fully obturate in any common-style rifling pattern, because of that deep 90-degree corner at the bottom of the groove/land intersection...

[Firebird]

Gain twist rifle (and pistols) barrels really ended for all intents and purposes when the round ball was dropped in favor of the conical bullet. A patched round ball engages gain twist barrels very well, anything else does start to leak gases around the bullet as the angle of the rifling changes. Gases leaking around the bullet causes metal fouling, whether lead or copper, and eventually destroys the accuracy. That may be one reason why the 460 isn't catching on, the other being it can't be marketed as the most powerful pistol cartridge like the 500 S&W is so a lot of the market goes to the 500 S&W instead.
Gain twist WILL produce the fastest barrels, as the bullet does gain most of it's velocity in that first couple of inches where the twist is least and providing the least resistance to the bullet.

[Dan Cash]

FWIW The U.S. Army uses a 30mm gatling type cannon, the barrels of which are rifled gain twist. Of course the rotating band on the projectile is only about 1/4 inch thick.
Dan

[mooman76]

I pondered about a gain twist rifle before I ever knew there was such a thing. Apparently it didn't work out or at least wasn't an improvement over the old method. An after thought I could see why it probubly wouldn't work because the angle of the rifiling must change as the bullet goes down the bore which would mean a small amount of stripping of the rifling would have to happen.

[shooter93]

They do work but in sporing arms it's a matter of degree. I built a 220 Swift Ackley using a gain twist barrel. It starts at 1/24 and end in 1/8. I have gotten some impressive velocities but I'm not convinced it's any more accurate than standard twist barrels. Just something I wanted to try and I don't regret doing it but I don't think it's a super barrel. Works for artillery though.

[runfiverun]

the reason is that a portion of forward momentum is lost to twist,
up to 30% or so airc.
if you have a boolit swaged to size and moving up or near velocity.
then rotate it it will be easier on the bbl, what you donot want to do is cut a gain twist back.

[Heavy lead]

Thanks for the replies, I'm glad I'm not the only one who thinks about these subjects. Think I'll stick to plain old rifled barrels for bullets and boolits.

[klw]

Gain twist rifle (and pistols) barrels really ended for all intents and purposes when the round ball was dropped in favor of the conical bullet. A patched round ball engages gain twist barrels very well, anything else does start to leak gases around the bullet as the angle of the rifling changes. Gases leaking around the bullet causes metal fouling, whether lead or copper, and eventually destroys the accuracy. That may be one reason why the 460 isn't catching on, the other being it can't be marketed as the most powerful pistol cartridge like the 500 S&W is so a lot of the market goes to the 500 S&W instead.
Gain twist WILL produce the fastest barrels, as the bullet does gain most of it's velocity in that first couple of inches where the twist is least and providing the least resistance to the bullet.

The 460 didn't sell, according to a friend at one of the major distributors, because of barrel failure. The barrels on the non-performance center were purchased from Germany I think and something was wrong with them. Exactly what I don't remember. But when the recall was made sales essentially stopped.

Also in an e-mail exchange that got pretty wide circulation someone asked Smith if it was true that their barrels, all the 460 barrels not just the recalled ones, wore out after about 1000 rounds of factory ammunition. Smith said yes. That didn't help the sales.

[DonH]

I don't know anything about a 460 cartridge much less why it did or did not sell. I do know gain twist barrels did not end with round ball use. The great Harry Pope made his barrels with gain twist rifling. One does not have to know too awful much shooting history to know of Pope's barrels reputation for accuracy. At the present time, the record for a ten shot group at 200 yds in ASSRA competition is on the order of .72", fired from a Ron Smith gain twist barrel. Those same gain twist barrels are with some regularlity shooting perfect scores on a 200 yd target which has a 1.5" center ring. Pretty impressive for low velocity (and fairly soft) plain base lead bullets. Any more questions about whether gain twist works or is accurate? Gain twist rifling is not necessarily (nor wasit in Harry Pope's day) more accurate than uniform twist rifling but it does work.

While often scoffed at in this country and not a target rifle, the Italian Carcano military rifle used gain twist rifling successfully with jacketed bullets at 2400 fps or so.

Respectfully
DH

[StrawHat]

DonH has it stated well enough when he mentions Harry Pope. There were others who used it also.

Gain twist rifling is similar to paper patching and dark beer, not to everyone's taste.

One of the semi custom barrel makers used GT rifling but stopped, it is too difficult to do on a demand basis even with modern tooling.

(I believe some of the early Trapdoors had gain twist rifling but that might be a confused memory.)

[jhrosier]

A relatively inexpensive way to experiment with gain twist rifling would be to find a M91 Carcano rifle.

Jack

[Bret4207]

Don H stole my thunder. Ditto what he said.

[klw]

More recently there was Gain Twist Barrel Company who made Ballard rifles for a while.

[405]

I think from what I understand about it... GT rifling, all other things being equal, has produced very good results. I also think that the theory behind it is just the opposite from the arguments about increasing stripping of the bullet. The theory was to decrease stripping as the bullet accelerated down the bore. Since the bullet at rest has inertia and wants to stay at rest both in forward movement and rotation.... the gain twist would be more gentle as the bullet is pushed from zero velocity and rotation during the acceleration. Also believe as others have posted the cost of producing gain twist is greater than constant twist and probably the reason it's not seen more often.

.... I think? :coffee:

[Wayne Smith]

405, as I understand it you are right, at least as far as Colt was concerned. The Patterson used gain twist rifling, the stated reason for this was so that the soft lead ball would not strip in the rifling but get a gentle start.