making replacement firing pin

November X-ray

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I'd use oil hardening drill rod first cut to within .005" oversized, then hardened and then wet gound to the final dimensions. Of course I am not a gunsmith by any means but I do tinker with guns and enjoy shooting on a weekly basis!

OH Yeah, I did stay at a Holiday Inn Express last week too!!!
 
I just made on a couple of weeks ago for an AR-15. I had on hand a piece of 1/4" Inconel 718. The original fp was 0.2485, so I simply polished a bit off, and my pin fit like I wanted at around 0.2493. Actual contact pin diameter was made 0.003 less than hole in bolt face. Original pin used radius transition of around 9/32 back up to the full 1/4" diameter. 3 jaw chuck on superspacer for milling retention slots. I took no pictures.

Several hundred round have been shot and there is no observable wear or other issues.

Of course, should you make one, it may work out just fine and you learn a bit. If you fail for whatever reason, then you could order one if you have to.
 
Since thats the case, I have some flat 4140 stock that I would use, but I wonder what the original pin was made from?
 
Looks like a good place to use an old power hacksaw blade. Makes good knives. Can Q & T as needed. Wouldn't want a fp to be too hard. All it's got to do is pinch a rim on a brass case. Careful rounding of the corners and edges of the contact point will be good.

Bobby Bailey might chime in here with some recommendations.

4140 is an alloy steel, hardenable. Very common. Not stainless

http://www.fordtoolsteels.com/pdf/LSS_4140-4142HT.pdf
 
are u sure the pin is flat? The drawing looks like there is a curve at the back. My guess is that it was a stamped part.
 
Firing pins for rimfires,for the most part, can be made out of anything, within reason :) 4140 will certainly work as will cold roll. w-1 and o-1 work well, but draw back about like a cheap screwdriver. Looking to get them a little tough, but not that hard. It is much better to have it soft than hard. Most firing pins fail to being too hard and breaking, too soft and they just batter. If the forward travel is arrested by a spring, a little soft will not be a problem. A little more toughness is needed if the pin is arrested by a hard stop. At any rate the finished fp should be capable of being filed. Try to match the factory tip shape and setting the protrusion from .025 min. to .040 max will normally work. Best if the fp will not contact the breech when fully forward. If I sound as confusing to you as I do to me, I'll try again. :)
Bobby
 
Looking good turbo if you are doing it for yourself don't worry about hardness just do it the first time to see if it works. The problem with rim fire firing pins is that if you dry fire a hardened pin on a barrel that i assume is made out of 4140, or ordnance steel it will start to peen over the chamber and you will have feeding issues and have to iron the chamber. I like to make my pins out of 0-1 and cut to size not worrying about final dimension for heat treating for it is not that critical that you could not polish it at critical points after you heat treat then draw it out to soften it a little. The only last tip that i can give is if you are making a round pin when you start to cut a new pin or are re shaping the pins for a smaller diameter such as on a remmy 700 it works very well to use a very very sharp piece of high speed and take small cuts.

Justin Bowerman
JB Enterprise
07 FFL in Central CA.
 
I suspect your desired clearance will be enough to make allowance for that variation, but on some things, that will be a pain. If you can move the vise to another position and take a few more readings. You may find a sweet spot that is acceptable.
 
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