According to R. O'Brian :
The standard rim thickness for the 22 rf is .044" Therefore the headspace
in a revolver needs to be .044" + enough to allow free rotation of the
cylinder. I don't have the industry standard dimensions to hand, but
.048"-.050" should be plenty. A real headspace gauge looks like a short
cartridge case with the proper thickness rim machined on it. They are
commonly made in Go and NoGo sizes. In practice you can use a cartridge and
a feeler gauge since the actual dimension is not too critical in a revolver.

BTW, the ratchet teeth do not determine indexing. It is controlled by the
cylinder bolt in the bottom of the frame window locking into the bolt
notches on the cylinder OD. Thus, the indexing accuracy is determined by
the accuracy of the cylinder machining when it was made.

But the ratchet teeth need to move the cylinder to the proper
point so the "cylinder bolt" will drop into it. If the notch is not in
line, then the hammer will fall with the cylinder out of line. If it is
a *lot* out of line, the firing pin won't hit the primer, so there will
be no real problem (assuming that your life is not depending on the
thing firing when the trigger is pulled), but if it is just slightly out
of line, then the cartridge will fire, and it will (at best) spit a lot
of lead out one side or the other. With something as small as a .22,
and with as large a sensitive primer area (the whole rim), I could see
it being out of time by 1/2 the diameter of the bullet, which could be
quite nasty.

So -- make sure that when you are done, the locking lug
("cylinder bolt" above) falls cleanly into the index notch -- *before*
you ever put any ammunition in it.

Check what happens both with slow cocking and fast (as with
fast, it is likely that the momentum of the cylinder will spin it a bit
more, so the locking lug will drop in anyway as the notch tries to spin
past it).

And -- if it is double action -- see whether the behavior is the
same when it is driven by the trigger instead of the hammer (as wear in
the linkage between them could cause shifts in the timing, depending on
just how the indexing pawl is driven. Those that I have seen were
directly driven by the hammer, but a worn or sloppy bearing pin for the
hammer to rotate on could shift in different directions, depending on
whether the hammer is being pulled back by a thumb, or cammed back by a
trigger.)

So -- make sure that you know what it is going to do
mechanically *before* you let it fire live ammo.

Good Luck,
DoN.
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