Typically, how much clearance is there between a firing pin and the breech, where it pokes through?



I was looking through some old patent drawings on the web site of the U.S. Patent Office and found an interesting action by Aston. The Ruger No. 1 is obviously derived from it. I have to wonder, though, about one aspect of the design. It is a falling block; the firing pin is integral to the hammer; but the hammer swings on the underlever pin. It seems to me if the breech block fails to rise fully (due to, say, a bit of grit), the pin would likely drag on the breech, possibly causing a misfire.



I think I once read the old BP cartridge guns used a looser fit between breech and firing pin. This could be done with the lower pressures of BP cartridges.

Actually the Ruger is an adaptation of the Frazer action.
Good Luck!

I've not seen the drawings for the Aston. The Ruger #1, (and #2 & #3) are all derivations of the farquharson single shot design. It is no secret that this is a favorite rifle of Mr. Ruger (the farquharson), and the #1 was one of the designs he was proudest of.