Firing pin material and hardness
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  1. #1
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    Default Firing pin material and hardness

    I am getting a few requests to run replacement firing pins for what would be called "cheap" pistols. The complaint is the end that strikes the primer snaps off. By the looks of the metal they have been hardened. I am thinking they could possibly be too hard, some had fillet radii, some don't. I am going to send some samples to be hardness tested. What material and hardness would you recommend for this application, what do well made expensive guns use? Would 303 or 304 work or would they be too soft.
    The only pistol I own is a 22 and it shots rim fires or I would go test fire a few. Not enough requests to buy a gun (I would never buy a cheap one) and fire off $500 of ammo also.
    Last edited by Dualkit; 11-17-2010 at 12:28 PM.

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    Polish the pin with with some emery cloth and wipe it down with a little acid or cold blue.

    It is possable that just the tip of the firing pin was heat treated. If so, this may show up in how the acid or cold blue reacts.

    A fireing pin should have reasonable hardness where the hammer strikes it to avoid mushrooming, but it need to be soft enough to have good impact resistance. As hardness increases the strength of a material rises, but its ability to absorbe impact energy drops. A localized heat treat job, instead of full body can also be detremental in this kind of application. The boundy between heat treated and the normalized body is softer than either and is a great area for cracks to form and grow.

    I hardness tested a few antique shotgun fireing pins and was suprised how soft they were - Rc scale did not even regester and I had to go down to the Rb scale. Yep, no heat treatment what so ever. You dont need much hardness to dent a cap. You want just enough to withstand the impact of the hammer and keep the part ware down.

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    Smile What type of Firing Pin?

    You did not say if the pin was attached to the hammer, struck by the hammer, or the striker type pin. Replacement pins are available from several sources. I would order one and test it to see what the hardness is. I would guess that a broken pin was the result of too much hardening and not enough tempering. Regards, Clark

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    Pins that are not attached to the hammer. I am sending them out for hardness testing.

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    Probably case hardened. They won't register right on a Rockwell tester. It's a good combination of hardness at the surface and soft core for a tough shock resistant part. If it is breaking at the thin part that strikes the primer then it may have to much case at that area. It is possible with casehardening to harden some areas thicker than others.

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    What no one seems to be bringing up is what type of pistol is it? If it is a semi-auto perhaps something else is at fault.

    If it is a 1911 type of action lock, i.e. a tilt barrel then other things can cause the firing pin to get snapped off. Go to the range and take a look at the primers on spent brass of 9mm, 40 and 45. See the primer strike, stretched to an oval on some of the rounds. This is the firing pin being engaged caught in the primer when the action is starting to open. If it really grabs you will snap the tip of the firing pin off.

    Hot handloads will cause this problem to really stand out or mil-surp ammo that has really hard primers that don't "give" and let the primer stretch to an oval. Also a weak recoil spring will let the action open up when there is still to much pressure in the chamber.

    I am thinking it is something like this because you said you have multiple cheap pistols with the same problem

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    I've made firing pins out of spring wire (like hay rake teeth), or grade 8 bolts. If you anneal to machine, temper to full blue after hardening. Use generous radii for inside corners,and polish if possible to forestall fatigue cracking

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    I have no idea as to the manufacturer of the guns. I did get the hardness of the samples I sent for testing. The .22 caliber was RC42, the .38 was RC52, the 9mm was RC35.

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    I know several smiths around here that uses bolts in 10.9 or 12.9 for firing pins, these are quite hard without being brittle and are said to perform just as well or better than OEM.

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    Quote Originally Posted by Fulmen View Post
    I know several smiths around here that uses bolts in 10.9 or 12.9 for firing pins, these are quite hard without being brittle and are said to perform just as well or better than OEM.
    Is grade 10.9 an 18-8 (304) or similar strength steel?

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    High quality jigsaw blades (for flat style) can be ground into a nice firing pin. Just don’t overheat it during the process.

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    That's ISO strength rating for high strength structural bolts, I'm sure you can find a similar SAE-grade-

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    I have been shooting black powder cartridge rifles in competition for the last 10 years. Believe it or not, I have had my best luck making firing pins from gauge pins. Chuck it up, dress your wheel to match desired radii, and get to turning while keeping the pin cool. They polish up very nicely, and slide effortlessly in the breech blocks I've installed them in. I have yet to have one break. My oldest one is in a 45-100 High Wall.(spring return) It's going on it's 8th. season and I have fired thousands of rounds with it. When I take it out for cleaning and lube it looks almost as pristine as the day I made it. Good luck with your pin jobs! Don

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    Try making the firing pins from "S-7" tool steel. It is a shock resisting type of steel, used to make chisels, and punches for air tools. It is an air hardening
    steel that will serve well in this application. Send the parts to a heat treat
    shop that can put them in a controled environment furnace, to reduce scaling.
    Bob

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    Weatherby used 46 RC at the tip and ending up at 42 RC at the other end on Mk V firing pins I believe.

    That should give you an idea on top end hardness for fp.

    Glenn

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    I use drill rod, have made over 20 for the swiss vetterli and never broke or bend one yet. Use for other rifles also.

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    CannonBall,
    I would assume(dangerous thing to do), that you are using O-1 drill rod, and not W-1. I have used O-1, for firing pins in the past, with good results. The long skinny ones, with a tip dia. of .06" or so may benefit from the better steel, and prosessional heat treat.
    Onlinemetals.com has S-7 drill rod in numerous diameters, if the need arises.
    A safe and happy holiday to all,
    Bob


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