notebook: rifling grooves

TRX
September 21, 2013
I've been looking at some rifling stuff again. I'd known that during WWI and later various US military rifles had only two rifling grooves, and people said they shot just fine. I've also seen pictures of high-end target barrels of the same era with 6 or 8 grooves. Nowadays, 4 or 5 seem to be standard for most purposes.

But I started to wonder, if two grooves worked fine, why didn't rifle makers stay with that? They would be faster to cut and reduce cost, wouldn't they?

Hmm, maybe not. I'm sure there were several two-groove patterns, but the picture I usually see shows two very wide grooves. That means a wider chip and more force to pull the cutter through. In wartime, when speed was the overriding factor, this would be the way to go. But otherwise, I bet you're looking at more wear on the equipment from the higher forces and the chance of chatter unless the cutting edge is honed often.

Narrower grooves would use narrower cutters in sturdier holders, and would take much less effort to pull. There might be less chance of barrel distortion. And whereas military ammunition is guaranteed to be the same, the the rifling is fine as long as it works with that, civilians insist on shooting anydamnedthing they want, from soft lead plinkers to steel-jacketed dangerous game bullets. More grooves and edges probably help there.

True? False? I'm just the guy with a theory...

TRX
September 23, 2013
I spent some time querying Google Patents last weekend. Looking for something else, I nevertheless came across dozens of patents for gain twists, some from before the Civil War, some in the 21st century. As patent documents are written in Intermediate Obfuscese, I was unable to tell what made each successive implementation unique enough to patent; as far as I could tell they were all describing the same thing.

A handful of bolt-action military rifles have used gain twist, but otherwise it seems to be the province of the black powder guys who shoot plain lead bullets.