How Heavy a Firing Pin is Too Heavy?

Post by **hcpookie** » Mon May 07, 2007 3:51 pm

I was wondering about firing pin designs, and it occurred to me that I could probably increase reliability by using a lighter metal, or perhaps using a lathe to reduce the area in the middle that is "free " in-between the ends of the bolt carrier.

What are the weights of the firing pins we have now? Since an AR and FAL both use a relatively small firing pin, I wonder if some of the light primer strikes people suffer (including myself!) can be blamed on too much mass for the hammer spring to overcome.

I've been having light primer strikes, all from SA surplus ammunition. I'm certain I've cut enough of the bolt carrier extension to let the hammer clear fully. I have quite a bit of play in there and the hammer completes its travel as the pin is hit - I'm confident the hammer is behaving correctly. I was going to search for a heavier-duty spring then I realized could achieve the same results with a lighter pin. I even thought about using a titanium rod for a firing pin, but I'm not willing to spend the money. I have an AK firing pin that is fluted - that would be a nice little addition!

I think this would also help to eliminate slam fire issues (double-taps) since there is less mass, and therefore less inertia, during the feeding cycle.

Thoughts? It couldn't hurt, right?

Post by **Pirate** » Mon May 07, 2007 4:10 pm

The main thing you need to eliminate is binding of the fp. the bolt, locking wedge and carrier are all floating, when the bolt locks up the wedge can cock to one side causing binding., that is one problem with a one peice firing pin. you can also have binding problems from the ejector extension in the bolt extension.

another problem can be caused by a loose grip, if it is wobbly it will reduce the hammer force on the firing pin.

Post by **bolex** » Mon May 07, 2007 4:44 pm

Too much weight in the firing pin can cause slam firing. Military ammo/primers help prevent this from occuring. Spring loading the pin is one way to prevent that from happening but that does reduce the hitting power of the pin. The optimum is a light, stiff firing pin.

propos · Post by **propos** » Mon May 07, 2007 6:04 pm

I thought about going the titanium route but I abandoned it. I made a pin from titanium. It's around somewhere. But I felt that the titanium wouldn't hold up. js412000 made a titanium pin but he said it was unsatisfactory.
My money is on the 2 piece pin for reasons which I have exhaustively discussed before. My 2 piece design has worked very well so far. There is a balance between the strength of the pin spring, weight of the firing pin and the power of the hammer spring that must be found. The only primers I had trouble popping were the Yugo primers. But part of that was I believe caused by the top of the hammer rubbing on the recoil spring upon release. I turned the spring so that the factory end is against the buffer assembly. I haven't had a chance to see if that has corrtected the problem yet. If not then a heavier hammer spring is in order.

Post by **Pirate** » Mon May 07, 2007 6:21 pm

I am working on an upgraded design to eliminate the binding problems, both with the ejector extension and bolt carrier alignment.
I have metal coming to make up a couple to test.

Post by **bolex** » Mon May 07, 2007 7:43 pm

Titanium is not a good material to beat on. Because the MG42 SA design uses a fairly large diameter pin, you could use a tube for the shank and silver solder/weld a a solid steel tip on both ends. 90% of a bar's strenght is in the outside material so the center material is dead weight.

js412000 · Post by **js412000** » Mon May 07, 2007 9:48 pm

I am using a two piece firing pin,and tried a fluted rear firing pin,but it was not light enough to make any improvement.
I made a titanium rear firing pin and it cured my slam fire problem. It seems to be holding up, so far, but I have not fired it enough to determine if this is the ultimate long term solution,in the areas of durability and reliability.
I am working on a spring loaded ejector system,as suggested duy annother member. I have the parts made and they just need to be heat treated and fitted.
I am still not happy with the entire semi-auto design, especially in the firing pin and ejection areas. The current designs work reasonably well, but are not nearly as robust or reliable as necessary for a commercial product.

Post by **hcpookie** » Wed May 09, 2007 10:05 am

Good discussion! The behavior of my two pins make me wonder if the SA .308 I'm using may have excessively hard primers.

I did have some binding I discovered around the hammer and around the bolt carrier. That was eliminated, and like I said, I do in fact get correct operation and primer fires, but only about 1/3 of the time. On a whim, I found a thinner steel rod and drilled it for my 2-piece pin setup. Surprisingly, it fired more often than the "full size" steel rod! I can not use the thinner rod because I used it to practice on my lathe and it is simply cut up way too much to be relied upon as a firing pin extension. I am going to put the rod in the lathe and thin down the middle section, or perhaps flute the rod. Or both!

I designed my pin as a 2-piece in order to use the original firing pin which is inserted into a hole on the end of the "extension". I figure that if the firing pin ever wears out, I can swap in a brand-new "factory" firing pin with this design. The extension is just a steel rod that is just the right length to extend through the bolt carrier (about 5 inches?).

I wonder if a steel tube with a thick wall may be a good candidate? I'm not sure how the firing pin would be fastened but tubing would be significantly lighter that a solid rod, and arguably stiff enough since it is only about 5 inches long. HRM...

Post by **haseo8up** » Sat May 12, 2007 1:21 am

Information only here for what I used. I use a modified version of pirate's design. The firing pin extension I turned in a lathe is .600" longer in the front, and I cut .600" off the original firing pin. Made it lighter and elimated slam fires. I have tried wolf .308 to reloads and no more slam fires useing non arsenal primers for reloads. That is what I want as a design for reloaded ammunition.
The pins in the picture are three different designs, left being a one piece, the middle is pirates design, and the right is the design I have described above. It works like a champ.
I have used SA .308 and I come to the conclusion that they have very hard primers. I could not reliably fire them in my SA 42, even useing the FAL FCG.