I have the following setup as my “M4” type carbine:
Noveske 14.5" midlenght bbl
BCM M16 auto BCG with wolff spring & Crane O-Ring.
H2 buffer
ISMI spring
RRA 2 stage FCG (soon Geissele SSA)
Runs like a champ! But every time I strip the BCG for maintenance, the firing pin retaining pin its beaten/deformed. Not much deformation as I can remove it from the carrier fairly easy, but enough to need to be reshaped with a pair of pliers in order to install it again.
I read a long time ago in TOS a thread about this. Apparently it has to do with the hammer hitting the firing pin during the “action”. If I can recall correctly there was a pic indicating where/what to do to resolve this issue.
Is there is a fix for this? Which of the above components is causing this? Out of spec firing pin protruding too much?
As always any help will be greatly appreciated. Thanks in advance.
The firing pin retaining pin should be very slightly spring tempered if it is correct. Many are not. Replace it with a correctly specified item.
In addition the firing pin needs to be an M16 unit with the large flange diameter as opposed to the smaller AR15 pin. The larger flange bares more squarely on the retaining pin when the carrier changes direction.
Finally the retaining pin should be rotated so that the legs lie one above each other. the wire section is thicker this way and the pin resists deformation better
I dont know how, but found I was using an AR15 firing pin in my M16 BCG. Somehow I managed to exchange it without noticing. Thats the problem with cleaning multiple AR’s at the same time and not been aware there was a difference between AR and M16 firing pins :rolleyes: . I guess one of my shooting buddies is running a M16 firing pin without even knowing it cause my other 2 AR’s have the correct M16 firing pin/BCG.
I replaced this AR15 firing pin with a M16 one from my spare parts kit. If this fix the problem, I’ll replace the firing pin retaining pin aswell just for peace of mind as this pin had been reshaped too many times.
Other thing, a couple of months ago I put together a spare parts kit for my AR’s. I bought almost everything from Bravo Co. I noticed the M16 firing pins they sell are DPMS. Just want to know people opinions about THIS PARTICULAR PART and the DPMS quality. Just curious because I’ve read a lot of DPMS hate lately in TOS. Actually this is the only thing DPMS I have.
That is strange. It SHOULD NOT BE HAPPENING, especially with Shrouded Carrier.
I know this problem used to pop up a lot on TOS with guys who had aftermarket Fire Control parts like DPMS and such. But generally they had a ramped carrier.
I’d be reluctant to address the problem with another aftermarket gadget.
I’m 99%convinced this problem was caused by me for exchanging firing pins by mistake. I noted the M16 firing pin have a larger diameter flange and a flatter head (where the hammer hits). This week I’ll shoot this rifle in order to prove (or hopefully not, disapprove) my theory.
About the firing pin retaining pin itself, it will be replaced with another milspec retaining pin, but I want to first solve the issue and then replace the retaining pin. The retaining pin posted by Rmplstlskn looks beefier, but I want to solve this problem at its very cause, not just use a tougher pin, but thats just me. Rmplstlskn, thanks anyway.
Anyone able to post a side by side pic of an AR firing pin and an M16 firing pin? I’ve heard they were different but don’t know what to look for. Can the M16 fp’s be used in a semi auto?
This is the first negative feedbacks on this item I have ever seen… Normally the feedback is “no problems” or “no deformations” etc…
Otherwise…
I just checked out my all COLT BCG used in my Colt-barreled M4… It is half-round with a RAMP, not shrouded. It has an M16 firing pin (not original, as my original succumbed to the pit caused by various pierced Winchester primers I had during handload tests before I switched to CCI primers).
The firing pin lip, while looking through the retaining pin hole, is just over 50% the diameter of the pin. An AR15 firing pin I have is just less than 50%… The difference is in the thousandths of an inch area…
My retaining pin had a good gouge from the firing pin on one of the legs… Maker of the pin is unknown, but was bought somewhere from a reliable vendor, so an inferior pin is unlikely. I have also periodically replaced this retaining pin as it gets banged up enough for concern…
The face of the “H” LMT buffer also has surface marring…
My M4 is not a COLT FACTORY build, but rather a build from “munyguru” on TOS. He had a builder he trusts build it and then they refinished it all in a dark black, so it is a PARTS GUN technically.
If this deformation is not NORMAL for an M4 with a ramped, 1/2 carrier BCG, then can someone suggest where the problem lies? Gas port size?
First a BCM carrier is shrouded meaning it’s not the firing pin that cocking the hammer it’s the carrier (the way it should be, the original design of the system).
On unshrouded carriers it’s the firing pin that cocking the hammer not the carrier. (the non preferred method).
The non shrouded situation is where the ‘fix’ is suggested. (adjusting cocked hammer height).
Like Bill Alexander says if the FPRP is installed correctly (both legs touching the firing pin) then it will last much longer. FWIW I find that FPRPs made by Yellow Tavern to last the longest.
I’ve only ever seen buffer face damage from 2 things:
Either an uneven surface of the bolt carrier (easily fixed), or from an improperly machined lower receiver (buffer retainer pin drilled too far rearward). The 1st means just knocking the edges off the carrier and lightly sanding the back edge of the carrier. The 2nd requires a new lower.
Looks like I need to break her open and take some pics of the buffer and retaining pin… You guys are pretty busy on SAT, so it is probably not a good idea to bring it in personally for you to look at…
It is a MEGA Gator lower, BTW. Usually well respected for quality… but a dud is always possible.
I also remember MG mentioning that the builder checked the gas flow after installing the PRI gas block sight and “opened up” the barrel gas port “slightly.” I had thought this pin and buffer face marring was from the port being opened up a bit too much. :rolleyes: Otherwise, this M4 has NEVER had a failure not due to ammo or magazine.
