Best min bc gap?

S&W factory spec for bc gap is 0.004".

S&W factory spec for bc gap is 0.004".

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That seems about right. You could go as low as 0.002, but you run the risk of binding the cylinder after a few dozen rounds of crud build up on it.

My new j-frame is about 0.006 with a few hundred rounds through it. Thats good enough for me.

Factory spec is .004" to .010"