Revolver tapered bore

R

RevLimiter

Inactive
Forgive my naivete as I'm none to familiar with the workings of revolvers and actually pistol or rifle barrels. I was cleaning my Ruger SP101 2.25" .357 earlier and I noticed a few things I hadn't before. While the entire cartridge will fit in the proper end of the cylinder, as it should, only the projectile can fit the other direction. Naturally this is no surprise. What did surprise me however is that a cartridge can fit about 1/8" up the lip of the brass in the bore before stopping. The bullet actually has lots of wiggle room at this point. When I go to put the bullet through the muzzle it goes in about 2/3 of the way before coming to a stop. This would lead me to believe the bore is tapered. A little research lead me to a term called squeeze bore where the bore compressed the bullet and increases velocity. Though after a short search I didn't really find anything about it being used in rifles or pistols. Let alone a revolver. Perhaps someone here can clarify this?
 
The rear of the revolver cylinder is the chamber and the entire cartridge should fit in until the rim stops it.

The front of the revolver cylinder should not accept the entire cartridge. If you get the chambers really clean and look into them, you should be able to see that there is a tapered "step" near the front of the cylinder. So the hole in the front of the cylinder is smaller than the hole at the rear.

The rear of a revolver barrel/bore, the part adjacent to the cylinder, is called the forcing cone. That portion of the barrel is tapered for a few mm until the actual rifling begins.

It's rare for the rest of the barrel to be tapered. It is true that some .22LR guns have a "choked" barrel that is made with a slight constriction near the muzzle. Usually that's in rifles. I'm not aware of any revolvers that have choked bores.

The bullet/projectile won't go all the way into the muzzle because the rifling actually engraves the fired round. It takes a good deal of force to drive the bullet through the bore and if you have a fired bullet, you can see how the rifling is pressed into the surface of the bullet, leaving permanent depressions in the metal.
 
If you ever do find a revolver that will accept the entire bullet, up to the mouth of the case, in the muzzle end, that's a good indication that the barrel is worn.

On the other hand, if a revolver will NOT accept the entire bullet, at least up to the case mouth from the front end of the cylinder, that's an indication that the chamber is not properly dimensioned and that it is swaging the bullets down too small as they exit the chamber. That typically results in poor accuracy.

I should probably have also mentioned that in some older revolvers, the cylinders might be drilled the same diameter all the way through, without the tapered step near the front of the chamber.

I don't know of any makers that are doing that these days except when the revolver is chambered for a caliber with a "heeled" bullet such as the .22LR. In those calibers, the bullet diameter is the same diameter as the case, with a rebated bullet "heel" that fits inside the case. Of course, when the case and the bullet are the same diameter, either end of the cylinder should accept the bullet up to the rim.
 
Cylinder mouths can be and have been all over the place in their
dimensions.

As for barrels, the Colt Python was famous for having a very
tight bore, a bit larger toward the rear and then tapering
down toward the muzzle. Colts were known to "shoot harder"
than Smiths which have/had more generous barrel bores.

IIRC, Smith cut their barrels for the basic .356 to .358 bullet
dimensions in jacketed and lead. Reportedly Colt cut their
barrels for a .355 bullet which is nominally the 9 mm
dimension.

Cartridge wall thicknesses also have been quite varied.
Some of the cheaper so-called range or target bulk
ammo as in .38s can be quite thick compared to the
more quality cartridges which being thinner expand
to seal the chambers better. I never liked Winchester
white box .38s for reloading.

On the Smith Forum, I mentioned that years ago
a writer cited the dimensional variations of a typical
revolver. Looser to tighter chambers, chamber mouths,
variations in the bolt lockup notches, again more
variations in the forcing cones and then the barrels
themselves. Again the cylinder gaps vary.

He said it was a wonderment that
revolvers are so dang accurate!

Today some newer shooters, when they send their
guns back to the factory, are miffed when what they
perceive as something that needs fixing the factory
says is within specifications.
 
An undesirable condition in a revolver is "thread choke" when the barrel is torqued so tightly into the frame that it squeezes down the I.D. at the rear.
The bullet is sized down as it passes through the tight spot and is too free in the barrel the rest of the way. Loss in velocity, less accuracy, and leading is obvious in severe cases.
The constriction can be lapped or fire lapped out, or the barrel Taylor Throated with a long smooth groove diameter throat.
 
"Colts were known to "shoot harder"..."

Only by Colt salesmen. Colt bores were/are not tapered or rifled to other than industry standards. All manufacturers make reamers/cutters to the maximum size, then sharpen them as they are used until they reach the minimum dimension, after which they are discarded. So no company reams its barrels or chambers to an "exact dimension" unless they use a reamer only a few times, which means either they charge a lot for the product or they go broke quickly.

Jim

P.S. Tapered bores have been made ("Halger" being an example, and some anti-tank rifles) with great claims, but also great cost.

JK
 
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