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Posted: 5/27/2009 7:45:57 AM EDT
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Looking for a little help. My dept. is running LMT's with standard bolts. Full auto for SWAT and semi for patrol. The patrol rifles have about 2k rounds thru em as they are pretty new and dont see heavy use.
Issue is one tooool noticed the indentation the firing pin makes on the primer of a cycled round. It does not look like a heavy dent nor does it look like the fireing pin is protruding excessively. It's been a few years since armorer's school... Am I correct to assume it the intera of the fireing pin causing the dent? All of them are doing it. New and old. My 5.56 and 6.8 that were loaded at home have the same dent in primer cups. I have to make sure these are good to go so –– what's the best way? Fireing pin protrusion gage? Anyone know the spec? Any advice is welcomed. Yes, I will be calling LMT later. Thanks in advance. |
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dont worry it's normal.
every AR do that 
ETA: the firing pin moves freely inside the bolt; when you chamber a round it touches the primer, but it doesnt have enough force to ignite the round. Most weapons use a spring on the firing pins to push them out of contact with the primer; with a AR this is not necessary due its well balanced design. |
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When you say cycled round, you mean a round that is chambered, BUT NOT FIRED, then extracted?
From my understanding, it is normal to see a small dent in the primer. Its a free floating firing pin, the momentum on the fire pin as the BCG slams home will carry it forward and it will contact the primer. The primer won't detonate without a forceful deep strike that can only come from the hammer properly striking the FP. Compare FP strikes of fired cartridges and cycled NON-fired cartridges. Look up the threads about slam fires, IIRC one of the first mods to the platform when it was fielded was to lighten up the firing pin to reduce the chance of slam fires even more. You'll see a lot of people tell you, slam fires are pretty much NOT an issue in the AR/M16, they are extremely, extremely rare even though the free float fire pin does contact the primer. Remember, standard safety rules for any firearm is to have it pointed in a safe direction when chambering/loading a round. |
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Quoted:
Thank you all very much. This was my experience and thought as well. MY problem is now I have to MAKE SURE it's good to go. Only way I can think of ensuring everything is cool was the fireing pin protrussion gage. Going to have to order 1  to make 100% sure you could replace all firing pins with quality ones. having the gauge wont hurt of course |
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You'd be replacing FP's that had nothing wrong with them. NOT very efficient or cost effective, which most Police Departments would aspire towards.
I'd get the gauge, use it to spec all the weapons, and you now have irrefutable proof to tell the toool that won't believe you that the marks are normal, to go pound sand. |
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Quoted:
Thank you all very much. This was my experience and thought as well. MY problem is now I have to MAKE SURE it's good to go. Only way I can think of ensuring everything is cool was the fireing pin protrussion gage. Going to have to order 1 Let me know what you find. |
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