Thread: 45-70 firing pin diameter

My google skills have let me down this evening.

I'm after some real world data on .45-70 ( or similar old school 40k psi cartridge ) firing pin diameter and protrusion ?

I have an existing firearm that I will re barrel in 45-70 and pressure will be around 40k max

The existing firing pin diameter is 0.083" in good condition and reasonably tight in its hole.
Protrusion is around 0.060"
This is a firing pin that will seal off the gasses at its base if there is a ruptured primer so gas will escape across the breech face rather than back through the action

I know that a modern firing pin for something like this would maybe be 0.070" diameter.

Just wondering if anyone has any useful info on this subject ?

Apologies for the inches ... but the more I dig into these old guns, the more I find myself having to use inches and fractions rather than metrics

hmmm dont think it will matter... surely the donor actions origonal chambering had similar if not greater pressure to deal with...for what its worth I fire the old cartridge through a .12ga action without issue so far.....my thinking is IF I ever stuff up and get a blow back there is plenty of area around shotgun action to vent out excess.

Originally Posted by Micky Duck

hmmm dont think it will matter... surely the donor actions origonal chambering had similar if not greater pressure to deal with...for what its worth I fire the old cartridge through a .12ga action without issue so far.....my thinking is IF I ever stuff up and get a blow back there is plenty of area around shotgun action to vent out excess.

Yes the wrist of the stock would shatter and take the energy before it gets to you

@homebrew.357

Originally Posted by akaroa1

My google skills have let me down this evening.

I'm after some real world data on .45-70 ( or similar old school 40k psi cartridge ) firing pin diameter and protrusion ?

I have an existing firearm that I will re barrel in 45-70 and pressure will be around 40k max

The existing firing pin diameter is 0.083" in good condition and reasonably tight in its hole.
Protrusion is around 0.060"
This is a firing pin that will seal off the gasses at its base if there is a ruptured primer so gas will escape across the breech face rather than back through the action

I know that a modern firing pin for something like this would maybe be 0.070" diameter.

Just wondering if anyone has any useful info on this subject ?

Apologies for the inches ... but the more I dig into these old guns, the more I find myself having to use inches and fractions rather than metrics

The 45/70 case is similar to a .303 british. You check LE firing pin protrusion by seeing it fits into a No 1 Mk III SMLE rear sight notch.