Gain twist in revolvers other than 460XVR?

Mouse · Apr 26, 2009

Designers explained that they had to do gain-twist rifling, because otherwise the projectile could be damaged.

But wouldn't any any long-barrel revolver benefit from gain twist, avoiding the initial loss of energy when the bullet hits the rifling? Why aren't all our revolvers (6" and longer) gain-twist rifled? It may not be strictly necessary - but it seems to be always beneficial (for long barrels)?

Mouse · Apr 26, 2009

Designers explained that they had to do gain-twist rifling, because otherwise the projectile could be damaged.

But wouldn't any any long-barrel revolver benefit from gain twist, avoiding the initial loss of energy when the bullet hits the rifling? Why aren't all our revolvers (6" and longer) gain-twist rifled? It may not be strictly necessary - but it seems to be always beneficial (for long barrels)?

john traveler · Apr 27, 2009

The original Colt SAA had gain-twist rifling. It's an old concept, and some rifles designed around the turn of the last century (Japanese Arisaka, Italian Carcano, etc) used it.

Gain twist rifling is most useful in medium automatic cannon calibers, where the relatively large mass of the projectile needs to be gradually spun up to muzzle velocity twist rate. Spinning it up to full twist rate at the chamber throat is hazardous because the projectile may "skip" and skid across the rifling losing all stability. Not at all good for high explosive warheads and autogun mechanisms. The also have relatively long barrels to develop the needed muzzle velocities.

In small arms handguns, the idea has lost favor except for a very few large caliber high velocity designs. The S&W 500 and 460 comes to mind.

Mouse · Apr 27, 2009

John, I really appreciate the information. But my question stands: gain twist would provide <u>some</u> benefits even when it's not a necessity (like in .44 Magnum). So why isn't it used as a routine? Why did this idea lose favor?

is it that much more difficult to manufacture?

john traveler · Apr 27, 2009

Gain-twist lost favor in pistol caliber small arms because it gave no advantage to conventional full-twist rifling and was more expensive.

And yes, it is more difficult and expensive to manufacture. In pistol barrels for instance, it required a single-point rifling cutter, and repeated multiple (many) passes and special cams on the rifling machine to accomplish the gain-twist. S&W has used broached rifling for their pistol barrels for well over 100 years. Gain-twist rifling can not be done using broaches. Nor can the more recent hammer-forged rifling machines.

Medium caliber auto cannon makers use chemical etching to make the gain twist, and large caliber cannon still use single point cutters. Both are specialized and expensive processes, but for the limited production of these weapons, is the established technology.

G-ManBart · Apr 27, 2009

While it's not a revolver barrel, Schuemann barrels makes incredible 1911 barrels with gain twist (AET models). I've got one in a .38 Supercomp (rimless .38 Super with a bit of additional meat in the web) racegun and one in a .40 S&W 1911.

AET stands for accuracy enhancing technology. A while back some PPC shooters sponsored by a big name gun company worked to do some accuracy testing with a barrel fixture to see what was actually possible. The only barrel they found that was capable of 1" groups at 50yds was a Schuemann AET.

They have a few other features besides the gain twist, but that's the big selling point. R,

reerc · Apr 28, 2009

Originally posted by john traveler:
Gain-twist lost favor in pistol caliber small arms because it gave no advantage to conventional full-twist rifling and was more expensive.

And yes, it is more difficult and expensive to manufacture. In pistol barrels for instance, it required a single-point rifling cutter, and repeated multiple (many) passes and special cams on the rifling machine to accomplish the gain-twist. S&W has used broached rifling for their pistol barrels for well over 100 years. Gain-twist rifling can not be done using broaches. Nor can the more recent hammer-forged rifling machines.

Medium caliber auto cannon makers use chemical etching to make the gain twist, and large caliber cannon still use single point cutters. Both are specialized and expensive processes, but for the limited production of these weapons, is the established technology.

I will confess that I'm completely outside of my knowledge base here, but would hazard a guess that it boils down to sheer cost, and return on investment from the manufacturers perspective.

Gain twist in revolvers other than 460XVR?

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