I've heard officially acceptable flash gaps run from 0.004" to 0.014". I'm mostly interested in knowing S&W's maximum.

Gil

On good authority, I am told that S&W now considers 0.012" barrel-to-cylinder gap to be acceptable.

0.006" is considered optimum. A little less and the chance of cylinder binding from firing residue is greatly increased.

There was a time not too long ago, that S&W sold new revolvers with b-c gap regulated to 0.005" to 0.008" and held cylinder endshake to less than 0.001". I guess those "good old days" are long gone.

Years ago (in the late 70's) the Factory Repair Center General Manager told me anything around .005" +/- .002" was in Spec. Now days, it's what ever they can get away with. I would personally be upset with a B/C gap of more than .006". Not that the revolver won't work, but you will start loosing velocity and encounter lead spitting. My revolvers ( which are mostly from 1950 to 1990) are all .006" or under. When I go to look at a used S&W I always bring a feeler gauge of .006" with me to check it before buying.

Chief38

In my S&W revolver armorer class we were told the acceptable B/C gap is .004 - .010.

The ones I've seen myself have tended to run on the smaller end of the range.

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Ret LE Firearms inst & armorer

.012" acceptable??? Holy smokes! That's downright offensive. Time was, that figure would tell us that the frame had been stretched. If that is correct, I really hate to hear it.

I prefer .005" to .007". I don't like less than .005" because that makes it too easy for a little leading to cause cylinder to barrel drag DA plus there's the ocassional unburt powder flake or ball. I've not experienced any negative affects form larger flash gaps but I may not have owned one as large as .010".

What prompted the question is a project. I bought a couple of .38 special cylinders hopping one could be used as a conversion cylinder in my 9mm 940 with no alteration to the collectable 940. Because .38 special headspace is less than the thickness of 9mm moon clips they require a lathe cut to clear the 940's cylinder stop. The best fitting .38 cylinder has great carry up but has a .014" flash gap with its yoke holding it snug against the breach face. It's at my smith for the lathe cut and perhaps a little headspace relief that would close the gap a hair. The smith had to grit his teeth admiting that the B/C gap would be O.K. for firing standard pressure .38 specials. I don't like a sloppy B/C gap either but the alternative is to scrap the project and resell both cylinders. I'm hopefull that the 940 will work out as a convertable because back in the 1980's a machinest friend returned a 57 that he had recently purchased new expecting S&W to warranty repair an .011" flash gap and customer service shipped it back unaltered telling him their maximum tolerance was .014".

S&W max..014 is ok if you are only going to shoot powder puff loads. Full house loads and you will flame cut the top strap. Fit at .005 you can always open it up if your not happy. Sure hard to put it back ie setback time,maybe thats where you are anyway on this project.

My .357 magnum and my .38 special are both .006 and neither one of them spit lead, nor do they bind up after shooting large amounts of rounds. I like .006.
Peace,
gordon

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better have that checked

My armorer manual says the same thing (004-.010 inch).

I don't want to be shooting along side anyone with a air gap over .010 inch. I don't want the side of my face flamed off! Spitting revolvers draw blood sometimes.........

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NRA Benefactor Member

I alway set mine to .006 on my guns. The larger gap spit some lead.

Almost all new S&Ws are at .006. I have a few that are about .004, and some that are about .008. I like them at .004. Ruger makes all theirs at about .003-.004, and usually have a little endshake , even brand new........Wonder why?