My buffer is getting chipped. From what I’ve read it can be caused by the retainer pin hole being drilled incorrectly or the upper being out of spec. The upper is a PSA and the lower is an Anderson. The retainer hole looks correct? The barrel also looks to be set deep enough in the receiver.
Any guidance on what I should look for or next steps would be greatly appreciated.
Getting chipped around the perimeter of the buffer, correct? When the upper and lower are together, does the BCG touch the buffer? You can usually feel it when you close them together or when you pull the charging have back. When closed, under normal operation the buffer never hits the retaining pin because the BCG holds it a small amount rearward of the pin. From your picture it looks like the buffer is slamming into the retaining pin. That will eventually break the pin because it’s not designed to take that sort of impact for long.
Yeah it’s getting chipped around the perimeter. When I put the upper on the lower I can feel the carrier push the buffer back, and I can see the buffer push slightly away from the retainer pin (although I’m not sure how far back it should be off the pin).
Does the retainer pin location look ok on the lower? I’ve just been looking at pictures and it seems to be, but I’m not sure.
Thanks for your response @BradE
It doesn’t have to push it back much. Just enough so the buffer doesn’t hit the pin. What does the back of the BCG look like? Is it scuffed or scratched? The pin and barrel look like they’re located ok. Is the retaining pin damaged? The buffer damage, that’s not just paint flaking off, is it? It’s actually getting scratched or gouged?
If it isn’t slamming into the retaining pin. I wonder if the buffer is rattling in the buffer tube and/or sliding around on the back of the carrier. If you were to remove the recoil spring, does the head of the buffer seem undersized in the tube? It shouldn’t be tight, but it shouldn’t rattle side to side either.
Maybe check the face of the bolt for burrs?
Seems to be a slight nick on the back of the BCG (bottom right). I have no clue if it’s enough to cause the issue?
I would like to see a picture of your buffer. Just the buffer, outside of the tube. Also what kind of tube is it? Kind of looks like the buffer is bottoming out as the rifle is fired and the BCG is slamming the buffer to the rear too much. Is you rifle over gassed?
there also looks like some scuffing or damage on the threaded end of the buffer tube? Or is that just the flash from the camera?
Have you tried switching bolt/bolt carrier group. You may be a victim of Tolerance stacking. Other than the mentioned retainer pin hole location, problems may be caused by too short barrel extension/too shallow barrel cavity in the upper. Too short dimension from bolt lug face to bolt cam pin hole. Cam slot in bolt carrier may be cut too far back. Cam pin may be undersized. Bolt carrier too short. Placement of retaining pin holes in upper and/or lower may be a bit off.
The back of the carrier seems overly worn or polished or something. Like it’s been ground against something. Was it new when you started? It looks pretty rough. I’m not home to look at mine but that wear pattern looks odd.
I agree.
Mil Spec tube. The rifle seems to shoot a little harder than other rifles I’ve shot, but nothing too crazy. Brass is thrown 3 o’clock. The threaded section of the buffer tube doesn’t have any damage that I can tell, just the lighting.
Here is a pic of the buffer. You can see the two indentations that look like they’re from the pin.
I haven’t tried switching the bolt or carrier, but I definitely will. I’ll take some measurements as well of the BCG/Lower. I’m not entirely sure how to go about checking the upper, I was just visually going off of where the lugs were in relation to the ramps on the upper.
Thanks for your help @Marcel_01
I thought so too. It was new when I started, and doesn’t have a super high round count.
Who made that buffer?
It’s from the classic PSA kit.
https://palmettostatearmory.com/psa-16-5-56-nato-m4-carbine-classic-rifle-kit-olive-drab-green-516446411.html
OK, I did a little searching around and found an answer on the M4carbine web site and similar issues on other sites as well. Turns out the buffer is supposed to stop and rest on the back of the BCG. Yours and many others of varying makes have a tolerance issue where the buffer doesn’t reach the BCG and instead rests on the retaining pin and damages the back of the buffer. Exactly like yours and I saw a few that were much worse. They had a solution, an offset stop pin that allows the buffer to go a little further to meet with the BCG.
https://www.m4carbine.net/showthread.php?188541-Buffer-damage-solution
I didn’t have this issue but I use an Armaspec SRS and remove the stop pin altogether.
Thanks @Spider1. I’m wondering where the tolerance issue is at (short BCG, retainer hole, or like @Marcel_01 stated, a possible tolerance issue on the barrel extension/upper). I’ll definitely check out the offset pin and try a new buffer.
Appreciate all the insight from everyone.
I had a very similar issue with my Ruger AR-556 (Complete rifle, not a kit). The buffer had multiple dents around the perimeter.
I found an offset buffer retainer pin made by Galloway Precision. Offset Buffer Retainer for AR-15 Rifles
Before changing the retainer pin, I checked the upper by pulling the pivot pin & the takedown pin to see if the buffer pushed against the bolt as I pushed rearward on the upper. It did not. After changing the pin, I could feel the buffer engage the bolt when closing the rifle, & with both pins pulled, I could feel spring resistance from the buffer as I pushed rearward on the upper.
The link to the buffer pin mentioned in the m4carbine forum no longer works. Galloway makes good stuff.
Test the fitment of the upper/bolt/buffer by pulling the takedown & pivot pins out. While holding the upper & lower together as if they were still pinned, relax your grip & see if the buffer pushes the upper forward by about an 1/8th of an inch. If you have to physically push the upper back against the buffer to push the pivot pin back in, your bolt is engaging the buffer properly. If not, use the offset retainer pin made by Galloway Precision. Offset Buffer Retainer for AR-15 Rifles
