Uberti chamber dimensions

[Inman]

I cannot accurately measure the groove diameter of a rifled barrel but I have always known that the groove diameters of my Uberti percussion open tops was greater than the diameter of their respective chambers.

I stumbled across a list of Uberti barrel specifications on the Cimarron web site which confirmed my findings.

Uberti specifications.    Bore    Groove

.31 caliber......................31........325"
.36 caliber......................36........379"
.44 caliber......................44........458"

Chamber dimensions of three examples in hand:

.31 caliber=.319-.320"
.36 caliber=.375"
.44 caliber=.451-.452"

Now I'm no rocket scientist but I can add and subtract and these numbers tell me that there is a lot of daylight left around the ball as it is passing through these barrel's.

Is it not generally accepted that a revolver projectile should be the same diameter or .001" greater than the groove diameter of the barrel for best performance?

Why then the undersized chambers of the Uberti's? Is this just sloppy Italian gun making or did the 19th Century Colt percussion guns have these same dimensions?

I would love to know what you all think about this.

Regards,
Inman

[Flint]

I do recall the original guns did have very similar dimensions.  The original Colt 1860 required a 452-454 ball, which shaved a ring to .446-448, I believe, and the bore was at least 454 across the grooves.  That's why it works with a conversion to 45Colt cartridge.  The Navy has always shaved a ring seating a 375-380 ball, but the bore is 375, so bullets (after seating) have always been undersized (to the grooves).  The cylinder's bore of both the 44 and 36 are, with very little cleanup, the diameter of the 45 and 38 cartridge case now used.

Two things to consider, one is the soft, pure lead ball, which is expected to expand, even the conical will expand.  Note even the Colt cartridge bullet had a shallow hollow base.  Two, the military use expected the gun to remain servicable when fairly heavily fouled with black powder, and the deep grooves were expected to have a large fouling capacity, shallower grooves would become non functional too quickly.

The Minie ball in the Civil War Springfield was undersized even to the bore (lands) and hollow based (for expansion) to allow muzzle loading without a hammer when dirty.

[Inman]

the military use expected the gun to remain servicable when fairly heavily fouled with black powder, and the deep grooves were expected to have a large fouling capacity, shallower grooves would become non functional too quickly.

It was my suspicion that this might be the case. If you stuff enough fouling into that "daylight " around the ball as it travels up the barrel you just might get a gas tight seal after all.

Thanks for your reply.

Inman