Firing Pin Hardness

*MALICE*

*MALICE*

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Have to make a couple firing pins for a .22Lr rifle.

The factory/stock ones broke off on the tips (three pins, three different rifles, same model).

Case hardened or full hardened?

If case hardened, how deep?

If full hardened, what RC hardness?

The pin is .079" diameter at the tip.

I want the new pins to last a little longer than the originals.

They will be getting professionally hardened (not flame hardened in my garage ;) ) so what I tell them will be what it will be.

Go.
 
A very well respected US gunsmith told me he makes all his firing pins out of the springs that open car trunks of old cars (70's). I got mine from an old nova. They are about 3.5' long and 3/8" diameter, and they are straight with a 90 degree bend on each end. They cut nicely with carbide, and require no heat treatment.
 
Times 2 DG

If you don't want to go that road, drill rod or hard stainless rod work fine jus the way they are. They both work easily with carbide tooling.
 
You want the steel to be tough but resilient. The optimum hardness to get to that point will depend on the grade of steel you make the pins from. If you're getting the pins commercially hardened then discuss it with the shop. Tell them what steel the pins are made from and what they are being used for. And remember to remind them that even though the nose is being cushioned by hitting a hollow brass rim that the other end is being hammered by a ... well.... er... a HAMMER. So it's the other end and any bends, notches or other oddities in the shape that are being subjected to the serious shock loads. With that in mind I'd be highly surprised if they don't have some ideas for the optimum hardness to toughness ratio to go for. On the other hand if they look at you like a deer in the headlights tell them that it's sort of like a repeat use drive pin that has to survive being hammered without undue distortion. At this point if they still have the deer in the headlights expression sigh, pack up and leave. Find another shop where they have some imagination and likely associated skill and judgement.
 
Seems a fairly large range of ideas here.

I probably should have mentioned I will be using either 3/8" O1 or 4140.

They are both ~20RC in the annealed state.

I figured hardening them above 55RC would be too hard and likely cause them to snap like the originals. I was leaning more towards the mid 40's.

I could use 4140PH which is between 26-32RC but I was a little iffy on if that would be hard enough.
 
I use Grade 8 cap screws of the approximate diameter. The material machines very nicely with high speed tooling and the finished pins last and last and last.
 
I use drill rod hardened, and then tempered by holding in molten lead. The lead draws it back to a spring temper, and still leaves the pin hard enough. Never had one break again.
 
Might as well add my experience with making a firing pin as well.

I had to make a pin for an 1887 shotgun. Used O-1 drill rod, the first one I made , after hardening ( garage style...acet. torch & a can of oil) it was dropped on the cement floor...it broke into two peices like a piece of glass.

The second attempt made it thru the tempering stage (2 hrs in the wifes oven at 450 deg.) and has been in the gun for a few hundred rounds, still looks as the day I made it, no peening on the hammer end or flattening on the firing end.
 
fingers284 said:
The second attempt made it thru the tempering stage (2 hrs in the wifes oven at 450 deg.) and has been in the gun for a few hundred rounds, still looks as the day I made it, no peening on the hammer end or flattening on the firing end.
Click to expand...

Tempering O-1 at 450 deg. would make the firing pin too hard (62-62 Rc). Tempering in lead would give the firing pin a preferable hardness of around 50 Rc.
 
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