I am constantly amazed when I go to buy a revolver or analyze problems how little the collector or accumulator know about checking certain critical items on a revolver. I routinely ask sellers about Barrel/cylinder gap and point out that they can measure that with feeler gauges. More often than not I get some reply that says well I can see through it so it can be much or offers to check it with pieces of paper. Very few people have any idea of how to measure it nor do they have the tool to do so. You should know what it is and also have the appropriate tool to check the guns you want to purchase. Just for the record...back in the 70's and 80's the BC gap should run from .004 to .010. Then more recently, probably coinciding with the lock guns the spec was raised to max out at .012. You should know that you can make it wider but short of dismounting the barrel and do lathe turning there is no way to reduce the gap. When turning a barrel back the extractor rod must also be shortened the appropriate amount. That's why gauges are so important. Do you really want to spend your coin on a gun with a BC gap of .014 and put up with the poor accuracy that goes with it and the spitting lead that will be felt? I doubt it.

Here are 4 sets of gauges, and they include the ones from the S&W armorers kit, a set of spark plug wire gauges that are totally unacceptable, a set of flat feeler gauges that include all that one needs, and lastly a set of bent feeler gauges which would be find except they don't go small enough. If one buys flat feeler gauges buy a set that includes .004 through .010 and if you have one of the newer guns also get .011 and .012.

Factory gauges from the S&W Revolver armorers kit circa 1987. I think these need help as the give the extremes but nothing in between. Saving grace is they are narrow enough to work with J frames.




A set of automotive wire gauges that are great for spark plugs and cars but simply don't go small enough for revolvers.



A set of flat feeler gauges. They work great except for being too wide to work on J frames. Since I don't do much work on J's and have the factory armorers gauges I don't worry about it. If I ever do spend a lot of time working on J's I'll have to buy a set of these with the idea of cutting them down.



A set of bent feeler gauges that are fine for cars but don't go small enough for revolvers.




By the way when measuring, be sure to measure from both sides. BC gap is cut with a barrette file by hand and the gap is usually somewhat off, one side to the other which is not a big deal unless one side exceeds spec.

I also use automotive feeler gauges. Bend and/or cut down as necessary. If a burr is left after cutting them down, a light touch with a fine stone will remove it.

I've got a dozen or so different feeler gauges (Automotive, Machinists, Specialty, etc.) but years ago I bought a few Starrett Shim Stock Sets that have feeler gauge stock ranging from .0015 to .100 that allow the making of my own gauges in sizes and shapes I need for specific needs. They come in 12" lengths and are about 3/4" wide and you can even carry a few custom cut strips in your wallet for attending gun shows or just in case you run into a gun that needs to be gauged.

Good information. After talking to you on the phone, I went out and bought myself a set. Its an inexpensive tool to put on the gun shelf.

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Hank
SWCA 2945

("You should know that you can make it wider but short of dismounting the barrel and do lathe turning there is no way to reduce the gap.")

Not exactly true. If the gap needs to be reduced a few thousands (up to about .005), you can install a yoke washer, which are available from TriggerShims Brand Shim Kits
These work well with the S&W's that use the spring loaded yoke retainer screw, will have to do a little fitting with the older Smiths.
I have never ran into any problems with excessive space at the recoil shield, as long as you are talking no more than .005"

Increasing the space between the back of the cylinder and the recoil plate is a bad idea. That's called headspace and in that regard .005 that you mention is a lot of headspace. Excessive headspace can lead to damage and injury. The barrel turning idea is much better and proper way to deal with excessive BC gap.

Thumbs up on feeler gauges. On the other hand they tend to just confirm what my eyes tell me, either the barrel-cylinder gap is okay or it's not okay. Some other tools and lights are also helpful when evaluating a revolver.

Attached Images

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Scoundrel & Ne'er-Do-Well

A go-no go headspace gauge and feeler gauges are very useful things to have around. They are literally lifesavers for a revolver toter. The expanded, fifth edition of Jerry Kuhnhausen’s S&W revolver shop manual is handy, as well.

If you don't have feeler gages, keep in mind that plain copier paper is pretty reliably .004" of an inch thick, so one slice should go, two, maybe, three, no....

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Robert
SWCA #2906, SWHF #760

The drawback to paper is that the fibers tend to crush down so that while you may think it is one thing it could be thinner. Also copier papers and other types come is so many differents weights that getting .004 reliably is not really something that one should depend on. Using calipers it is almost impossible to measure it reliably due to the crush.

NO argument here, just in a pinch, McGiver style, you know.

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Robert
SWCA #2906, SWHF #760