My LMT lower works great but the buffer is getting peened by the buffer retainer.
I put in a new buffer and it looks like it was hit with a small punch 20 times after firing just one mag.
Is there some kind of fix ?
The buffer should not hit the retainer during normal operation.
That retainer is only there to hold things together when you remove the upper.
You can check this by watching the buffer and BCG as you slowly close the upper.
During the last little bit of of travel, the tail of the bolt carrier should push the buffer back enough so it does not touch the retainer.
If it doesn't move the buffer back, you need to figure out why.
Also check the tail of the bolt carrier for wear marks.
Do you have any other rifles to compare with?
Is this a new buffer, new lower? how about some other clues and history, pics?
check if the receiver extension tube is screwed in to far? I know when we made our SDMRs in Iraq we took m16A4s and put collapsible mod stokes on them on a few of them we had to adjust how far the tube was screwed in to the receiver to stop them from hammering of the buffers.
I have a buffer(rifle) with these marks also. This was an experienced buffer with life before me. It has always puzzled me of how these marks appeared as not from any of the upper/lower combos that I have put together.
You said you had a couple of ARs? Open up one of your other receivers and take a coupe of measurements to see if you tube is screwed in too far or if the retaining pin looks different. Like the other poster said, just shoot it if it's functioning okay.