I didn’t notice at first but I recently have noticed some wear marks on one of my ARs on the face of my buffer around the edge of the buffer. The rifle is a complete BCM upper with an Aero Pricision lower but with all BCM lower parts. This is my second build. When I manually cycle the rifle the marks will appear around the buffer retaining pin.
When I slowly mate the upper and lower I can see the BCG push the buffer back off the retaining pin like it should but the marks will still appear on the lower edge were the buffer retaining pin is.
I know my Colt 6920, a Bushmaster and my other AR build doesn’t do this. So I decided to swap uppers, buffers and springs, and mix BCG’s to see if I can isolate it and I found that it was one BCM BCG that would leave the marks on the edge of the buffer face but when I put a second BCM BCG or even a Bushmater BCG then no marks. So Im thinking a bur is on the end of one of my BCM BCG maybe? Any corrective action needed? I just hope I didn’t missed something like maybe its an out of spec lower worst case scenario.
Make sure that the carrier takes the preload of the action off the detent with the upper and lower assembled. It’s easy to mistake preload when pivoting on the front pin. Verify that the carrier fully locked takes the preload off the pin when sliding the upper and lower halves into assembly held together without the take down pins engaged. There should be no contact between the retention pin with the buffer when assembled.
Just got home work, and I was able to verify that the BCG does in fact take the preload off the retaining pin. Also I held up both my BCM BCG to the light and I was able to see two rough edges that visibly were sticking up just ever so slightly at the tip of the ratianer relief area of the carrier(don’t know the actual name)of the one that was suspect. After that I took the buffer with the marks on it and I changed the orientation of it to a side that didn’t have marks yet and put the carrier with the burs in it and racked one time. Low and behold there was two marks one on the left and one on the right of the retaining pin further confirming that its not the retaining pin itself nor the lower or upper.
It is a bit suprising that a BCG from BCM would have burs on it given their stellar reputation for quality. But I’m not knocking them at all I know mistakes can happen with any company and I will continue to be a BCM fan and recomend to to everyone I know. I basically answered my own question but I figured I’d share this hoping it would be helpful to anyone else who might have a similar issue.
You would be misled or mistaken to think that companies examine every single part for stuff like this. It may be unsightly, but it’s ging to have very little impact on function.
Ironically I am experiencing the same issue with my 10.5" and Vltor A5H3. Can someone go into more detail in explaining the carrier/preload aspect to look for?
Interesting. I really never gave this a second thought, but I do have a buffer that looks beat up. I just chalked it up to high round count. Time to investigate!
My only concern is if it may damage the buffer in some way leading to some issue down the road. But at least its an easy fix, ether file off the sharp edges or get a new BCG problem solved. If it was an out of spec lower that would be a headache.
A cheaper and easier solution would be to simply locate the offending areas on the carrier and deal with them before assembly. If you can “feel” a burr or whatever that would wear into the buffer contact area, deal with that issue.
Honestly this kinda sounds like a complaint that the inside of your tail pipe turns black every time you go for a drive.
The amount of material needed to form a burr on the aft end of a carrier that would eventually cause a buffer to fail would be almost impossible to miss. The face of the buffer is so stout it would take an event beyond catastrophic for it to fail completely and send the weights into the action.
