View Full Version : gain twist BBLS

August 10, 2001, 05:19 AM
A couple questions.

#1-Why the gain in the twist?

#2-What calibers are commonly used in gain twist?

#3- How many grooves in gain twist?

#4- how many different types of gain twist are there?


James K
August 10, 2001, 11:52 AM
Hi, rr41Mag,

For those who may not be familiar with the term, gain twist in a barrel is a steadily increasing rifling twist rate going toward the muzzle. It was used in the Colt percussion revolvers and also in the Italian Carcano rifles. There are some modern barrel makers who will supply it on special order.

1. Some people believe that allowing the bullet to get started before it begins to turn reduces initial pressure. This would seem to have some logic, but AFAIK no one has conclusively shown that it means anything in terms of overall performance or accuracy.

2. Any caliber the customer wants. Probably 6mm and .30 are the most common, but I will defer to a barrel maker on this one.

3. The barrel maker usually uses his normal rifling, but the number of grooves is independent of the twist rate.

4. If you mean what are the ratios, I think that depends on the maker and the customer. The rifling can start with no twist and go to, say, 1:10 at the muzzle.

Making a barrel with gain twist rifling can be expensive, and, as noted above, I do not know that anyone has proven any advantage to it.


August 10, 2001, 04:13 PM
The test data I have seen on these new gain twist bbl.'s is that there are no major benefits to accuracy you get a little longer bbl. life though (a couple hundred rounds or so).

Jim V
August 10, 2001, 05:31 PM
Many a muzzle loader used gain twist barrels. Did the idea help, damifino.

August 10, 2001, 08:30 PM
You beat me to it, the only time I ever heard of gain twist barrels was in muzzle loaders. I didn't realize that any modern firearms had ever been produced using them.

4V50 Gary
August 10, 2001, 08:37 PM
was whether gain twist barrels were more accurate than the normal rifled barrel. Big shooting matches to prove it. Y'know wot? It's the shooter.

August 11, 2001, 06:41 AM
HMMMMMM ( while scratching the forehead ) I know an individual that wants a 6mm "cut rifle" gain twist BBL for his next rifle he wants to build. I guess thats what brought on the questions. Thanks very much for the answers by the way.

August 11, 2001, 08:51 AM
IIRC, some Enfields used gain twist rifling, but see no use in it really. I do know 20mm Vulcans used gain twist, but who cares about accuracy when you're spitting out 3,000 rounds per minute? The only theoretical advantage I could see on using gain twist rifling would possibly to use a hotter load while keeping pressures down, but I suspect that might be more acedemic than something you could really qualify.

James K
August 12, 2001, 03:01 PM
A few thoughts. Colt used gain twist in percussion revolvers; Remington didn't. No accuracy difference noticeable.

Another wrinkle that crops up from time to time is variable groove depth. This means that the rifling grooves start out at normal depth (.004 or so) and decrease to zero or close at the muzzle. The claimed advantage is that the bullet markings are smoothed out before bullet exit and there is less air resistance, hence longer range and higher terminal velocity. Experiments seem to show it works, but the cost of the special barrels outweighs any practical effect.

Yet another is the taper bore. This was done on some artillery pieces, especially those designed to penetrate armor. The shell is made to squeeze down to the smaller bore. The idea has been tried in rifles (Halbe and Gerlich) and produced high velocity but again the expense of making the barrels was too high for the idea to be practical.