My cousin just got his first arf about three weeks ago; a Bushmaster M4A3 with Mini-Y comp. We took it out then and ran the first 400 rounds through it, didn’t clean it then took it out again yesterday and ran another 400 rounds through it. So, the rifle was NIB, and ran 800 rounds through it without incident.

We take it down last night to clean it and find sharp edges around the large flange on the firing pin as it is exposed in a Sporter type carrier.

Is it normal that firing pins get chewed up like this?

Best regards, J

Normal.

Not unheard of, but I question whether it's "normal". Either the piece has an M16, large collar, firing pin in it, or the hammer is not catching in a far enough rearward position to avoid hitting the flange, or both.

My own attitude has always been to get rid of the POS, Colt designed politically correct carrier. All the major manufacturers, including Colt, have finally seen the light, and new production is coming off the line w/o the cutaway under the firing pin. Nearly 40 years too late, but I guess better late than never.[;D]

I would say its not normal and would swap out carriers with one w/o the cutout near the firing pin. Both my RRA and BM have the cutouts on the carrier but neither have that problem.
The hammer is hitting it.

Normal.
The firing pin is being peen'd on the back of the carrier as it moves back, then forward as it closes.  If the AR-15 used a spring to keep the pin back, this would not happen, such as on the AR-10.

The solution to get more life out of the firing pin is to take the firing pin, lightly chuck it up in a drill, then spin file the peen'd edge and slightly taper the leading edge at a 45* angle.  

Bottom line is that the pin will peen.  As the firing pin peens out, the hammer will start to catch the pin, and wreak havoc on the firing pin retaining pin (bend the shit out of it as the hammer catches/hangs on the pin edge on the forward stroke).  By beveling the edge, the metal has to peen/flow past the relieved edge, and the firing pin will not need to be replaced/shortened until the normal wear peening has caused the pin to have too much protrusion (.039 or more) out of the front of the bolt when struck forward by the hammer.

Very rare that I would disagree with anything Dano has to say in the technical area, but my class 3'd SP1 has over 25 years of use, many thousands of rounds thru it, and it does not have any of the chewed up edges described. Niether do any of the other ARs I have; because they all have fully enclosed carriers  The collars do have bright rings in the front from hitting the rear of the bolt, but that is the only sign of use on any of them[:D]

Shamayim,

Trust me, some of the firing pins on the market are softer than others.  Plus, no fair bring up hooded carriers, and carrier that have been milled completely flat at the back of carrier!!!!  

I have built on off-brand (read non-Colt) non-hooded carriers that the back edge of the carrier (where the firing pin collar strikes) that have wicked chatter burs from when the end mill made the end plunge cut and are less than a flat/level/smooth surface.

By having to make these “Fun” kits/parts work, I get to save some of the other guys the brain damage/time on figuring out how to tweak parts to make them work.  If all I every used was Colt parts, I would take the “Fun” out of building and then trouble shooting the little bastard rifles that I seem to spend most of my time working on.

P.S. I am not referring to Bushmaster as less that ideal rifles, just some of the other kits/suppliers that I have laid my hands on.