"T" Style rifling in .22rf barrels

[Frank Green]

Here at Bartlein Barrels, we have the capability to produce rifling twist rates in virtually any combination. Some will call it gain twist, progressive twist, incremental twist etc....for now we will call it transitional rifling or T style rifling. The rifling twist can uniformly be increased through out the entire length of the barrel or we can custom program any twist combination in to the barrel that the customer would want.

We've been asked by several rimfire shooters and black powder shooters if we can produce barrels like this. The answer is yes and we have done a few for these people. One customer has told me that in the .22RF he had or use to be able to get barrels that went from 1-16 to 1-15.5 at the muzzle said they shot like crazy but he hasn't been able to get anymore until now.

If anyone has used barrels like this in rimfire I would like to hear from and your thoughts please.

Any ways I've been asked about it several times so I decided to make a post on it. Any questions best if you email or give us a call.

Later, Frank
Bartlein Barrels Inc.

 

[David Valdina]

Twist progression I think...

I think most are a progression, going from a lesser twist to a greater twist as the bullet travels down the barrel. In the old days, with cast lead bullets and black powder, the thought was the "exposion" of the powder would cause the bullet to strip if introduced to a high twist right away. Starting it with a small twist, then progressing to a greater twist would allow the bullet's base to expand, make a good seal, get the bullet into the lands and groves and build up the rotation needed by the time it exited the barrel. I can not see any benefit in starting a .22 bullet out with smokeless powder at a 1:16 twist, then reducing the twist to 1:15.5 If you want 1:15.5 on the bullet in flight, have the barrel that for it's full length. I don't think bullet stripping is an issue with smokeless powder, which doesn't "explode" but only expands rapidly. But if it is, no harm in starting the bullet at a slow twist and progressing the twist as the bulet moves down the barrel. My 2¢ worth.

 

[David Valdina]

Me bad, senior moment...

After clicking "Post", I remembered that the smaller number is the faster twist. Boy, am I embarrased. Sorry about that.

 

[mhb]

Gain pitch rifling...

is, indeed, nothing new. However, it seems worthwhile to mention a few facts regarding such rifling:
1. Gain pitch barrels cannot be lapped to improve surface finish, so extra care is required in their manufacture - a bore-riding lap can be used on the lands, but the groove sides and bottoms cannot be lapped by conventional methods.
2. If cut-rifled, the width of the groove must necessarily change as the pitch is increased, since the aspect of the hook is changed with respect to the groove: a hook of given width will cut a wider groove at the breech and progressively narrower as the pitch increases. This might seem desireable in preventing the escape of gas, but will also deform the bullet more than fixed-pitch rifling will.
3. With reference to bullet deformation, the forces on the bullet surface are shearing ones which force the already engraved groove to change width and pitch - this cannot be desireable for best accuracy, particularly in the case of jacketed bullets. Soft lead alloy as in cast bullets is rather plastic, and can probably withstand the shearing forces better than hard jacket material, but the bullet cannot but be stressed more than necessary.
It is true that Pope and other makers of (usually) muzzle-loading cast bullet rifles used the gain pitch, but Pope himself used conventional rifling in his highpower barrels, and, in his case, because of his painstaking workmanship, it is likely that his rifles would have shot just as well had he used only conventional rifling.
mhb - Mike