Wildly uneven barrel-cylinder gap

[Hapworth]

K-frame that otherwise checks out well, but the barrel-cylinder gap is all over the place. By feeler gauge measurement, left side is definitely narrower than the right, so I'm pretty sure the barrel face is uneven.

But the gap also varies on each charge hole, so the cylinder face may be out of true, too.

Yoke doesn't seem to have any runout.

The numbers on each charge hole:

1 — left side, less than .0015" (low as the feeler gauge goes); right side, .004" (hint of rub on cylinder face indicating metal to metal on this charge hole)
2 — left, .002"; right .007"
3 — left, .005"; right .009"
4 — left, .006"; right, .009"
5 — left, .005"; right, .007"
6 — left, .002"; right, .005"

Trying to decide what exactly I'm looking at and what to do about it, if anything. Primary concern's fouling lock up on that narrowest charge hole.

 

[Protocall_Design]

I've seen that on many S&W revos, but to a much smaller degree. The fix is to face off the cylinder on a lathe, and set the barrel back 1 turn, and make the back of the barrel square, with the proper gap. Not a big deal to do, but does take time and care on the barrel fitting.

 

[Hapworth]

I've seen that on many S&W revos, but to a much smaller degree. The fix is to face off the cylinder on a lathe, and set the barrel back 1 turn, and make the back of the barrel square, with the proper gap. Not a big deal to do, but does take time and care on the barrel fitting.

Yeah, I've seen small swings but this was surprising.

What're your thoughts on just squaring the barrel face and if it shoots calling it good?

 

[Protocall_Design]

That would leave you with a fairly wide gap, but still usable. You would be getting a lot of blast from there. The front of the cylinder would still be going in and out as it went around, possibly causing hangups on the closer part, but maybe not with the wide gap.

 

[WR Moore]

"Everything else checks out well.." does that include end play? (Back and forth motion of the cylinder.)

You mention "yoke runout"-I'm not familiar with the term, do you have a yoke alignment gauge? An out of alignment yoke could account for some of the variation side to side. If you have a way, you might get that checked first and if it needs corrected, you should start with that.

One time I had a model 57 in the shop with a 0.007 in variation in cylinder length. Easiest/cheapest way to cure that is a return to the factory. A surface grinder can cure that in short order, but why should you pay for it?

 

[Hapworth]

"Everything else checks out well.." does that include end play? (Back and forth motion of the cylinder.)

You mention "yoke runout"-I'm not familiar with the term, do you have a yoke alignment gauge? An out of alignment yoke could account for some of the variation side to side. If you have a way, you might get that checked first and if it needs corrected, you should start with that.

One time I had a model 57 in the shop with a 0.007 in variation in cylinder length. Easiest/cheapest way to cure that is a return to the factory. A surface grinder can cure that in short order, but why should you pay for it?

Good questions.

No end play on this one, and the yoke's true. If it were new I'd sent it to S&W but this is an older one and I don't let S&W work on the older ones anymore.