One of my revolvers has a gap of about .009/.010 ( measuring with the cylinder held back) but when I measure it after pulling/holding the trigger back (with snap caps), the gap is around .007.

I was thinking about having the gap tightened up a bit but now I'm thinking that I should just leave it?

Just leave it alone, it is well within current factory specifications. Even if you were to have the barrel set-back to .006 or less it is unlikely you would achieve any improvement in either accuracy or velocity. I have set back barrels from ca. .010" to as little as .002" to see how much improvement in velocity I would realize and the difference before/after over the chronograph was exactly 000FPS.

As long as it is shooting OK and not blasting back at you I would tend to leave it alone. I confess to liking the old specification (.004-.006) much better than the current specs which are much more generous, but that's just me.

Thanks for the responses.

Nothing blasting back. Also, the timing, lock up, and alignment are all perfect.

I just reread the a post on how to properly measure the gap / end shake (quoted below) and according to those instructions, my gap is actually .007/.008 with around .002 of end shake so well within spec.

"When initially checking your revolver you should start by pushing (& hold) the cylinder forward & then measure the gap between the cylinder face & barrel breach.

Next you push (& hold) the cylinder to the rear & re-measure that gap.

(Admittedly it doesn't matter which you check first. The rearward reading will always be the larger (maximum) reading.)

The forward reading is B-C gap & the rearward reading is B-C gap plus (any) endshake.

Any difference between the two readings is the end shake.

You have to do both checks to come to a meaningful understanding. If you do one without the other you do not have the whole picture or all the details."

I was curious about what (if any) increase there would be in velocity so that's good to know.

Basically, you have a barrel-cylinder gap of around 0.009", which is within S&W limits, and end shake of around 0.002", which is also within S&W limits. Nothing really to worry about unless you experience bullet spitting from the gap.
Since you mentioned the relationship between velocity and the barrel-cylinder gap, you can read about an experiment at this link.
BBTI - Ballistics by the Inch :: Cylinder Gap

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