Material for firing pin

[johnm1]

What material would be the best to machine a new firing pin from? Mild steel or stainless? If mild steel, would the surface the hammer strikes need to be hardened or heat treated? Stainless would certainly be strong/hard enough, but more difficult/expensive to machine. I would think I could have several machined from mild steel for the cost of one in stainless. The firearm is a S&W 916T shotgun. I am aware of all of the weakneses of the firearm. I have already fixed the feeding issue. And as is fairly commen with this model, the firing pin broke in two. It must happen often as none of the parts sellers have one in stock. With layoffs In the near future I would rather not replace it if I can make it function reliably. It is what I have and working properly is exactly the firearm I need for a turkey hunt this fall.

[Bill DeShivs]

I would recommend 1095 high carbon, heat treated to spring hardness.
Mild steel will deform. "Stainless steel" is simply steel with added chromium. While there are versions of stainless that would be fine for a firing pin, heat treating them is difficult for the novice.

[T. O'Heir]

Hi. Firing pins are daft things. They have to be hard enough to smack the primer, but tough and exactly the right length too. Mild steel is out for hard and tough. Doesn't heat treat right. Tried it for a .22 FP. SPS maybe.
SS is an alloy with enormously different properties by the alloy. SS is hard on cutting tools as well.
Try these guys. http://www.lsgmfg.com/
You see this? http://firearmsid.com/Recalls/FA_Recalls%205.htm

[HiBC]

Here is an idea.I do not know your shotgun,or how much machining is required.I have found mold core pins,for plastic injection molds,are a useful resource.They are made of H-13 tool steel,and prehardened.They come in two hardnessesThe softer ones are fairly easy to machine with carbide.The harder ones can be machined with carbide,but its more difficult.They grind nice I don't recall exact hardness,but I think one is about 38 C and the other about 50 C.Look to MSC,mold core pins,read what is available.

[Harry Bonar]

Sir;
1095 indeed would be O.K. - it contains 95 points of carbon so it, indeed, could be hardened and then temper drawn to about a brown color at the tip and blue on to the end.
Lasalle fatigue proof steel Brownells sells would be good to. I've made 98 mauser pins out of 4140 and they've worked well.
Harry B.

[mete]

4140, 4340 hardened to HRc 40-45 would work well . There was on company that made firing pins of tough beryllium copper !
I you make a pin make sure it's machined very smothly and if there's a step make sure there's a good radius , no sharp corners. Tip should be rounded [sharp edges tend to tear through the primer]

[johnm1]

Thanks all for the replies. I think I found the 1095 on Brownells page. I have time on this one, so a little more reading on the Lasalle and 4140 and I should be able to do this.

Tony - I had looked at LSG but they don't list the pin at all. I figure the only way to get one is to buy an entire bolt. That would cost almost as much as the current retail value of the entire gun. I planned to call them on Monday but expect that they just don't sell/have them. At least as a separate unit. And yes, I had seen the recall years ago. My barrel has the 'O' indicating that it was originally shipped with the revised barrel. I had repaired the cartridge cut off years ago as a lot of owners have in the past. It has sat unused since then. Actually this gun functioned well for the first couple of years until the cartridge cut off issue occurred. It was only this year that I noticed that the firing pin was broken.

These things had a terrible history. I understand gunsmiths wouldn't touch them because the things would break while in the shop for another repair. I have until the first of October to repair and field test for reliability. Hopefully it will be as reliable as it was for the first 3 years. If not, the Mossberg 500 is economic enough for a replacement.

May yet have questions as i get further into this.


Thanks again.

[dahermit]

What material would be the best to machine a new firing pin from? Mild steel or stainless? If mild steel, would the surface the hammer strikes need to be hardened or heat treated? Stainless would certainly be strong/hard enough, but more difficult/expensive to machine. I would think I could have several machined from mild steel for the cost of one in stainless. The firearm is a S&W 916T shotgun. I am aware of all of the weakneses of the firearm. I have already fixed the feeding issue. And as is fairly commen with this model, the firing pin broke in two. It must happen often as none of the parts sellers have one in stock. With layoffs In the near future I would rather not replace it if I can make it function reliably. It is what I have and working properly is exactly the firearm I need for a turkey hunt this fall.

Low carbon steel would bend and deform with use. High Carbon steel in the form of Water hardening and Oil hardening Drill Rod is readily available. I used to buy it from a local auto parts suppler and they would give you a specification sheet that came with it. The sheet had the break-down of elements making up the content of the steel and more importantly, the temperature and procedure to heat treat (harden and draw temperatures)it to achieve the desired properties. Without the data on how to heat treat, you are in the dark or have to rely on suggestions here as to temperatures and heat colors and hope for the best.
Something as small as a firing pin, it would be easy to get it too hot (way over 1333 degrees F.), resulting in the grains growing and having a weak (likely to break), result. Or, not hot enough (less than 1333 degrees F.), to harden. I used to over-heat drill rod samples and then quench, break them in half with a hammer, correctly heat and quench samples, and show my students the difference in the grain structure of the broken steel. Proper heat treating procedure can be tricky.

[johnm1]

Thanks Dahermit,

Heat treating is the reading I am going to do. I do appreciate the lead on the auto parts store and the data sheet. Brownells does supply information on the hardening and tempering for the materials they supply. If I can find it locally I will, but I figure Brownells can supply what I need with the appropriate information. Learning what to do with that information is the next step. Of course I don't have a controlled furnace but I understand that there are materials that can be used in the process that help indicate when the required temperature is achieved. Learning about that is the next step. Harden is easy to understand. Draw is a concept that I am unfamiliar with.

As it turns out, there is a seller on Gunbroker that makes these. He is just out at this time. I did send him a message and he is going to check with his tool maker to see when they are going to make them next. Purchasing a completed part would be the easiest outcome.

[James K]

I always used drill rod for firing pins, but now Brownells has "fatigue proof" steel rods that sound like a better material. Has anyone used that for firing pins?

Jim

[Bill DeShivs]

If you use 1095 or any of the 10 series steels, or 0-1, I can help you.
Just ask here.

[johnm1]

Thanks Bill. I may take you up on that. 1095 is the easiest to get at this point. But I have not tried any local sources yet.

It turns out I found a replacement firing pin. NOS (or from a part gun) I think. I may still fabricate a couple. There is a reason they are hard to find. They break often. And I think I can learn something here.

The plan is to procure 5/16" stock material and bring the broken piece to one of two machine shops I deal with here in the Phoenix area. Both have worked with me in the past on small projects. They don't do them right away, but they get done. My plan is to have them mill the part on the lathe and do the finish and heat treat work myself.

I searched for the fatigue proof steel rods on Brownells but haven't found it yet. I may call them tomorrow as well.

[James K]

I don't recall ever having had one of those apart and I am not sure I have ever seen one, but from the diagrams, the firing pin looks like pretty easy lathe work. If the guys you work with don't charge three arms and two legs, having a couple of extra made might not be a bad idea. FYI, Gun Parts lists them at $13, plus s&h, so a reasonable shop charge might work out OK.

Jim

[johnm1]

The lathe work consists of 3 different diameters and a channel for the retaining screw. All but 1 cut is square. The single cut from the smaller diameter firing pin to the larger diameter strike side needs to be "beveled". Not sure bevel is the correct machinist term. This is the weakest point and where mine broke. The original has a flat after the bevel at this location for the return spring to land that I think I will leave off. It will give the bevelled joint just slightly more material. I can't imagine the return spring will suffer resting on the slope of a bevel cut instead of a flat.

[mete]

As I said "good radius, no sharp corners" .Sharp inside corners are often causes of early failures !!!

[dahermit]

I understand that there are materials that can be used in the process that help indicate when the required temperature is achieved. Learning about that is the next step. Harden is easy to understand. Draw is a concept that I am unfamiliar with.

At 1333 degrees is when the Ferrite becomes Austinite and is non-magnetic. Therefore, if you heat the high carbon steel (1095, drill rod), with a torch until a magnet is no longer attracted to it, quench it in salt water, it will be at its maximum hardness. However, it will be too hard and be too brittle to use (and may even crack when quenched or if not drawn immediately), in that state. The part must be drawn (tempered), by re-heating it to give up some of the hardness (and brittleness), for toughness. The part is buffed to remove the oxide that has resulted from the first heating and quenching so that the "silver" color can be seen. It is then re-heated and the heat colors are observed to indicate how hot it is. When the color of the metal reaches "straw" color, the part is quenched again to end the process.
This is a somewhat crude "shop" process...the absolute best way would to have the proper heat-treat furnace to control the temperatures, but shop rats have been using this method (or variations, including drawing in burning oil, temperature indicating substances, etc.), for years with good success.

[mete]

Hardening temperatures are usually 75-100 F above the Curie temperature .Light oil would be better quenchant .No need to quench after tempering ,just remove from heat. Better tempering would be in a toaster oven for 1-2 hours.

[Bill DeShivs]

Canola oil seems to be the best readily available quenching oil for HC steels.
Brine (salt water) will almost guarantee the piece will crack.
I would temper the piece to just past blue. Straw may be too hard. A toaster oven is a good thing to use-especially if you have a good thermometer in it.
550 degrees for a half hour should be good.

[dahermit]

Brine (salt water) will almost guarantee the piece will crack.

Water hardening drill rod is intended to be quenched in brine. Yes, some pieces will crack, and that is why early data sheets warned that, even though using water hardening drill rod and brine would result in a product that achieved the maximum hardness (harder than oil hardening drill rod), it was "risky", meaning that a certain percentage of pieces would indeed crack.
The salt in the quenching water is supposed to keep the bubbles that form on the surface of the part very small instead of forming larger ones that would tend to insulate the metal from the cooling water, assuring a more uniform hardness throughout the part.

[dahermit]

Canola oil seems to be the best readily available quenching oil for HC steels.

Good to know...I searched in vain through industrial supply catalogs for quenching oil. Never found any for sale.

[dahermit]

Just a note: For those without access to sophisticated heat-treat resources, it is likely better to avoid the temptation to use a High Alloy Steel for small parts inasmuch as some of those require more sophisticated quenching medium than is available to most of us. Sub-zero quenches like Liquid Nitrogen...don't have much of that laying around.

[James K]

Maybe there is some kind of quenching oil, but I used medium weight motor oil and I don't think any problems were traceable to the oil. Of course I had springs break; maybe I could have blamed the oil if I had thought of it .

Jim

[Bill DeShivs]

I make a lot of springs and have for years. I use 1095 almost exclusively and I quench in canola oil. I have never had a customer return a broken spring.
Real quenching oils are expensive and not available in small quantities. Canola doesn't flare up or smoke too much, and you can buy it by the quart.
JamesK- your springs broke because they were not tempered properly, not because of the oil. You left them too hard.

[johnm1]

This subject becomes more interesting the more I read about it. I have gathered about all of the information from the internet that I care to (this forum excepted). Does anyone have a suggestion for a book I would be likely to get at the local library. I do live in Mesa, AZ near Phoenix so I probably have some decent resourses available to me.

Now for a dumb question. Can a piece of hardened steel be machined and still retain its hardness? I figure the heat generated in the machining process would work against the hardning. But if I don't ask I'll not know for sure.

[Unclenick]

I've made several firing pins from O-1. Works fine. Tempering temperatures and some other properties are here. Quench for O-1 is 1450-1500°F, and they recommend you heat the oil to 125°-150°F to avoid distortion and cracking. After the quench, you want to draw a firing pin back at 800°-900°F. That's a little tough in the toaster oven, but that Rockwell C scale hardness of around 45 to 50 is where you want to be to absorb impact without deforming, yet not be brittle.

I bought a gallon can of Brownells Tough Quench awhile back. Pricey but, if a gallon lasts as long as it lasts me, that's of no consequence. I'm not doing large parts. Special reamers are about as long as I get.

The fellow who builds muzzle loaders out here uses 20 weight non-detergent motor oil for his spring tempering, and rather than a second heat and quench, he pulls the hot steel out of the first quench and sets fire to the oil on it. Let's the flame draw it back.

For the firing pin, a couple of things: There is a phenomenon called 500° embrittlement in steel, wherein the strength actually declines between around 500° and 700°. You generally want to skip over that temperature range. I find cylindrical shapes that are long will warp easily in the quench, so I get a wire hook on them and spin them with a variable speed drill while I quench them. It seems to average the error out and they stay pretty straight. Maybe it just keeps the bubble from favoring any particular spot?