My dad bought a Khan shotgun a few years ago that seems to be pretty hard on firing pins. He really likes the gun because it fits him well, but the gun just isn't made from quality materials. Both firing pins broke about a year ago and my dad replaced them with parts sent from the factory. Now one firing pin has broken and the other has been shortened because the metal wasn't hard enough. My dad's Winchester Model 101 skeet gun has been fired at least thirty thousand times and has had no broken firing pins. From researching the company on the internet, Khan shotguns are cheap for a reason.
Anyway, my dad told me to find some replacement firing pins for his gun. I looked around but Numrich was sold out. So, I took a look at the firing pins and decided to make some on my lathe. Basically, it's just a bar with varying diameters and a notch. The shoulders align the pin and a spring pushes the pin back into the action, while the notch lets a "retainer pin" limit how far forward the firing pin can travel when stuck by the hammers. It's important to get this notch in the right place so the firing pin won't rupture primers. Here's a simplified diagram:
Conceptually, they're pretty easy to understand. However, I'm not a very good machinist so it took a lot of trial and error to make a pin with the right lengths and diameters. The first pin took about 3 hours to make, although the second pin only took 45 minutes. Once I was confident the pins would work, I had to harden them so they'd take the repeated pounding from the hammers. I'm no blacksmith either, so I simply heated them to bright orange with a propane torch and quenched them in old motor oil. You're also supposed to temper them after hardening, but I'm not sure if I did it right. I guess I'll just have to see how long they last.
In the summer of 2011 the bottom barrel stopped firing, so dad told me to fix it. I originally suspected it was a problem with my firing pins, but it turned out the factory sear spring had snapped. It's never a good sign when you take apart a gun and little bits of springs fall out. Replacing the spring was pretty simple, I just cut a ballpoint pen spring down to the appropriate length. It's a little weak, but it does push the sear into engagement with the hammer notch ok.
While I had the gun open I took a look at the firing pins I made a few years ago. They are slightly dented where the hammers hit them, but other than that they are in great shape and should last for a good while longer.