[warddc]

I am trying to figure out what you would consider the upper limit on cylinder mouth opening. The used M60 I just picked up is .362" What can happen (if anything) as the cylinder diameter goes up. At what point should the cylinder be replaced?

Dave.

[JoeHatley]

Dave,

Are you sure you didn't drop a zero or two? I've read the current S&W factory spec is somewhere in the .003 --> .009.

Joe

Nevermind Dave, I just re-read your post and figured out I was thinking B/C gap.

[Mike Irwin]

Do you mean at the front of the cylinder where the bullet jumps to the forcing cone?

.362 sounds about right.

Nominal bullet diameter is .357/.358. Much smaller and the bullet might be damaged in the jump, or squeezed down to the point where it's now too small for the bore.

Too large and the bullet will yaw excessively as it enters the forcing cone.

[BigG]

Elmer Keith did pretty extensive testing about the cylinder throats back in the 50s and 60s. Bigger is better than smaller IIRC since the bullet has to be large enough (at least bore diameter) to seal the gap between the bore and chamber to avoid gas cutting.

[tiberius]

The worst problem is when the chamber mouth is smaller than the bore. This problem plagued early .44-40 Ruger Vaqueros. Needless to say, accuracy was "somewhat" affected.

Yours sounds fine.

[warddc]

I talked to the fine folks at S&W and they said that spec on the cylinder opening was .357-.358 but not to worry about .362 I was curious at what point the cylinder should be replaced. They basically said it it ain't broke don't fix it. They never really gave me a max safe diameter.

dave.

[Old Fuff]

Ideally the chamber mouth should be .001 to .0015 inches larger then the barrel’s bore diameter. To tell the correct diameter on a particular revolver you need to slug the barrel with a pure-lead ball (of the kind used in muzzleloaders) that is slightly larger then the bore. With a .38 Special or .357 Magnum I would use a .360 diameter ball.

Clean the barrel, and then drive the ball through the barrel using a rod or dowel and is a close sliding fit inside the bore. Do not use a cleaning rod for this purpose. Catch the ball when it comes out the breech end of the barrel in a wadded cloth or similar so it doesn’t get dropped or dinged up. Then measure the diameter across the flat where the rifling is engraved. I would expect this to be between .356 to .359. You can use a larger lead ball to measure the chamber mouth using the same method, but driving the ball through from back to front.

I would say the chambers on your gun are oversized. You can expect additional pressure if a soft lead bullet is expanded to .362 and then squeezed down to .358 or so in the barrel. This would probably be less so if you were shooting jacketed bullets.

Unfortunately today’s manufacturers don’t seem to be concerned about what goes out the doors these days, but as a general rule chambers tend to be undersized rather then oversized.

[Gary H]

I recently paid S&W to replace the cylinder on my 45LC. I tried everything to improve the accuracy and reduced leading, but to no avail. I haven't shot the gun much since getting it back, but I'm hoping that the accuracy has improved and I have noticed a reduction in leading.

http://www.thehighroad.org/showthread.php?s=&threadid=34103&highlight=chamber