Gain twist rifling - pro's and con's

[GaryJones]

Anybody ever try gain twist rifling (like the new .460 S&W pistol cartridge)? Seems like a way to reduce chamber pressure by starting with a 1:12 and taper to a 1:8.5 and still be able to stabilize heavy for caliber bullets. Would it be possible to taper for 3/4 of the barrel length and then run the rest of the way out at your desired twist rate?

[Richard338]

I was thinking about gain twist rifling for my .338 LM. The problem is not whether the idea is good or not, but whether any of the top barrel makers do it.
The best known barrel maker who does it is Lothar Walther. Their rep told me I would have to order 5-6 barrels for them to do a production run.
To my knowledge, in big guns (155mm), the gain in twist usually follows an exponential.
I don't think you would want a linear gain in twist followed by a length of constant twist as you described.
The other thing is that you would want to design a specific bullet that you intend to use and then build it specifically for that.
If you don't get it right the first time, just order another 5-6 barrels...

[GaryJones]

An exponential twist would work even better in a gain twist barrel where only part of the barrel is taperred. It would be a smooth transition into the portion of the barrel with the standard twist. You would choose your bullet weight the same as normal, only with a reduction in pressure. Moly coated bullets would help (reduce friction), as well as a longer barrel length (a milder twist rate gain could be utilized. ie. over a 24" portion, as opposed to a 18" portion).