Cam Pin problems

[rabrooks]

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.....

[gunfixer199]

You need to either replace the cam pin and what caused the problem or take it to or send it to someone who is qualified to repair it. From just looking at the cam pin & not seeing the crack you are speaking of I can not make a qualified determination on the problem. However depending on what is going on with the firearm you may have an UNSAFE firearm. My I suggest you maintain caution with this problem.
gunfixer199

[PA Rifleman]

Wow! Your post sent me scrambling to check my cam pins.

From you image, both of your cam pins appear to be cracked. The wear pattern suggests high unit pressure at the top where it last makes contact with the bolt. While the term heat treatment pops up in my head, the very next item I'd have a close look at is the bolt. Consider measuring the cam pin bore in the bolt. I would also inspect the bolt pin bore for a burr or a annular protrusion near the top. The wear pattern is very unusual, and alarming to say the least.

Here's a cam pin from a 20+ year old M16A1 (right), and a 1984 Colt HBAR (left):

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Photos enlarge with a click

I believe both are original. The round count on the HBAR is unknown, the M16 has 10K + rounds through it.

The AR-15 cam pin diameter measures 0.311", the cam pin bore (in the bolt) is 0.315".

If I were in your shoes, that bolt & cam pin would get trashed at the speed of light.




BTW, you are aware what can happen if you have cam pin failure, right?

Life gets interesting when things like this happen.