haven't seen this before

**rabrooks** · November 14th, 2009, 01:08 AM

Stag Arms AR15, Mdl 1, 16", 2year old. PMC bronze 55gr, Mil Surplus 62g Grn-tp. Shoot once a week.
I was cleaning up after a trip to the range, I noticed that my the cam pin(in my AR) had suffered a new kind of wear. It seemed that a crack had developed around the lower third portion of the Cam Pin's body. It seemed that it followed the contours of the inside of the carrier. Just above the firing-pin hole going down on the sides, and then up and over the hole on the other side. I asked around and got several opinions. After calling the mfgr. I was pointed to the obvious. I had just installed a one-piece gas ring set. About two weeks before that I installed an Endine Hydraulic buffer. Has any one else experiencd bazzar Cam-Pin wear? Yeah I know. If it works.... I was trying to bullet-proof my AR. I've had several ARs in the military, but I've never seen anything like this! The origonal Cam-Pin(upper) has over a thousand rounds on it. The replacement(lower) had only 2-3 hunderd.(please excuse. my camara dissapeared, and I tried using the scanner) I tried putting my old gas rings in, but they now gave too much drag. I'm on my third now Cam Pin. Seems that the damage is diminishing. Any ideas? Thank you ahead of time.....

**Franchi20/28** · November 14th, 2009, 03:13 AM

It looks, to me, like somehow the bolt is moving too far forward in the carrier causing the odd wear patterns.

Bolt lugs out of spec? Too long and pulling the cam pin into the front of the cam pin groove of the carrier?

Bolt somehow going too deep in the carrier on extraction and smacking the end of the cam pin groove?

Is the wear on the front or back of the cam pin? Did you notice it before you lost track of the pins orientation?

Without those answers my best guess is somehow the new gas ring set is letting the bolt retract too far into the carrier.

Damage on both sides because you didn't notice it after the first outing?

Seeing less damage on new pins...the edge in the carrier that marks the cam pins is wearing (being beaten) down and interfering less with the cam pin.

Oh, by the way, I don't know shit about AR mods.

**Suburban** · November 14th, 2009, 04:20 PM

M4Carbine.net bolt failure thread - some discussion about cam pins toward the end of the thread

**rabrooks** · December 13th, 2009, 09:33 AM

Many thanks for the concern. Well, I took the simple route, and tried to reverse engineer my improvements. The first thing I did was to get a new bolt/carrier group. While checking all parts I noticed that the extractor on the new bolt moved with the application of moderate force. I also remembered that after the extractor up-grade, I could barely move the extractor.Popped out the doughnut, and things seem fine. Seems that the rubber/nylon doughnut was applying too much force on the extractor base. Due to inclement weather I could only get out a couple of times. While looking around I've seen several other extractor up-grade components. Maybe that's whay there are different versions.. Either way, I'll take a little longer before I can positively state that it was the rubber/nylon doughnut.