There was a thread about heat treating here a while back, but was not exactly helpful in my case. I have been machining replacement firing pins for my American Arms Silver O/U shotgun for a couple years now, and need to harden the hammer end of them more effectively. I am using either oil hardening or water hardening drill rod to make them. I thought I had a handle on the austenite-marsentite quenching point, but apparently not. I have been hardening the hammer end only. So, need some knowledge about how to do a more effective heat treat on this. Am I using the right steel? Would case hardening be a better choice? I still have some Kasenite in the cupboard for that. Oil, water, or air cooling the best option? The firing pins are stubby little things about an inch long and 1/4 inch diameter, the hammer end has a deep notch in the side, that presents a smaller strike face for the hammer. The hammer is peening this end. I also have issues with the original problem that started this ongoing project, the firing pins break at the taper point between the actual firing pin end to the main body of the pin. The receiver casting was not machined where the pins go, you can see casting roughness in there, including the shoulder the springs rest on, and there is really no way to smooth this area as it is not lined up for any reamer I have to get into the pin holes due being blocked in line by the remainder of the receiver frame. I would have to cut a reamer down to about 1/4 of its length to do that, if anybody thinks cleaning that area up might help to increase pin life. I use this for trap shooting, and it routinely breaks them after about a 1000 rounds, might last forever if I hunted with it and fired maybe a box full of shells every year or so.
American Arms imported these things from somebody in Italy, and it is a well made shotgun whose guts are identical to several higher end models, but they must have cheaped out on the firing pins. Picked this up at a gun show a few years back for a song, but in a month it failed to fire the lower barrel which led to the broken pin discovery. Parts are in the unobtanium category. Why not get another shotgun? I hate to be beat by a problem like this, and if I can solve it, I'll feel better about selling it and maybe then getting another shotgun. As many people that are out there looking for firing pins for these though, maybe start a cottage industry supplying parts. If anybody currently makes these, let me know and save me the trouble.