barrel/cylinder gap

[vzeoah]

Posted on other forums for those that might have already seen, but looking for some input...
A question. I watched a video by Larry Potterfield, from Midway. He shows how to get rid of excessive end shake in a S&W revolver. Correct me if wrong, but doesn't this do so by shimming the cylinder at the end of the yoke, thereby putting the cylinder always further back in the frame? In other words, keeping the cylinder/barrel gap opened up at maximum all the time? If I am correct, and have excessive cylinder/barrel clearance, isn't this is pointless?

 

[BBBBill]

Yes. All else being equal, the cylinder is moved to the rear by installing the shims. And absent any other adjustments, it will result in a wider (and more consistent) barrel gap. It must be seen in the context of the operational condition of the gun and the overall goals. Headspace can be corrected by installation of the shims as well as endshake. Ultimately, excess barrel/cylinder gap will rquire the barrel to be set back. What is excess is what you and your smith decide. The factory says that it is a given amount, say over ~.008", but I've seen guns with .013" function well enough as long as the cylinder alignment is correct and the forcing cone is good. Too tight and the cylinder will bind when it gets hot.
My experience is limited and others may have had other experiences. In a perfect world, I would much prefer to have:
1) perfect headspace
2) near zero endshake
3) the smallest cylinder/barrel gap consistent with reliable function.

 

[Oro]

Yes, adding a shim will increase b/c gap, and shrink headspace. The cylinder is a fixed length and so is the window, this should be pretty obvious as you've observed. But the nut of the issue is that there is a larger tolerance for b/c gap and headspace than there is for endshake. So you are borrowing from one to close another. This can be done once or twice, but not any more. It's an interim fix to a problem that eventually, with enough firing, requires a machining operation to fix.

If you have an excessive b/c gap, putting in an endshake bearing would not help it, of course. But putting in endshake bearings is not a way to fix a b/c gap (unless it's too TIGHT a b/c gap, which does happen sometimes). It's a way to fix an endshake problem.

EDIT: it appears BBBBill and I were typing at the same time. I agree with him and I think our replies say the same thing.

The factory says that it is a given amount, say over ~.008", but I've seen guns with .013" function well enough as long as the cylinder alignment is correct and the forcing cone is good.

I believe S&W is now saying around .012" and are not even rigid on that. They are shipping guns new with those b/c gaps, and they have in the past, too (I saw a brand new 1970 S&W 27 with a .012" gap. And it shoots beautifully). I agree with you that .013" is not unacceptable if everything else is tight and right. Sometimes people get obsessed with one number as a "holy grail goal" and loose track of the big picture.