See if your BCG has the same wiggle in another upper. See if a BCG from another rifle wiggles the same in your upper.

I'm betting that the upper receiver has wider tolerances than uppers from other rifles. Or it could be that the BCG is on the small side of a spec and the upper could be on the large side of the spec causing some tolerance stacking.

Tony.

curious if the cam pin is original, and how it looks,

Is carrier tilt an issue here?

I’m not seeing a problem here. I have similar looking parts in my rifles. 20,000 rounds on a buffer and it’s probably time to throw that buffer in the spare parts bin.

New buffer, new buffer spring, new or rebuilt bolt, new gas rings, new extractor, new extractor spring, and send another 20,000 rounds down range. If the trigger, hammer, and disconnector springs are original I would replace all the lower springs and check the trigger components for wear as well..

I’d check your recoil spring for proper length and number of coils. I have a 10.3” carbine I built. Had a problem with ejection and felt like it was really kicking more than my other rifles Turns out my recoil spring was almost 2” short in length and number of coils. Replaced it with a new flat wire carbine spring and heavier spikes tactical buffer.

The parts that contribute to the wear pattern you're seeing are the buffer tube, buffer, recoil spring, and bolt carrier. There is a chance that the rear of the lower receiver is contributing to the issue, but you'd see wear to the sides of the buffer, and the inside of the buffer tube if that were the case. You could try changing each part in turn, but the you'd have to fire enough rounds to see if the pattern comes back. I would just chalk it up to a tolerance stacking issue and be done wth it. As long as the gun is reliable I don't think there is a serious issue here.

I'd first look at a new action spring if you havent replaced it in a while. If that has no results then I'd consider a heavier buffer. Keep us informed, these things are interesting and useful to others even after they are fixed though I'm sorry you are having trouble.

Just had a thought, have you been using ammo that was made recently or is it older stockpiled stuff? We have noticed ammo made during the most recent panic has had more instances of issues and its possible the recipe might be just a touch off. Any cratering on your FP tip or wear on your buffer tail?

Thanks for all the comments.

This is the bottom of the BCG: nothing remarkable that I can see.





I have a replacement action spring. I will see if it makes any difference in the handling, but of course the wear on the buffer is already there. I’ll also watch the (new) FPRP, and I’ve marked it so I can tell which direction it bends. The spring is a Colt replacement and except for the slightly longer length, it’s identical as far as I can tell to the current one, including the number of coils.

Except for the wear on the end, the buffer looks fine with no damage to the tail. From a functionality standpoint I see no reason to replace it. The firing pin shows no damage either. I date mark my ammunition, and the most recent that’s been fired with this rifle was purchased in April 2012.

quote:

Originally posted by SgtGold:
I would just chalk it up to a tolerance stacking issue and be done wth it. As long as the gun is reliable I don't think there is a serious issue here.

That’s pretty much where I am at this point. As I mentioned, the rifle is my primary training AR and if it quits on me due to something I couldn’t figure out, it won’t matter much.

Thanks again for all the comments and ideas. I posed the question on the chance someone would see the pictures and say, “Oh, yeah: that’s due to an oversized frammis pin; that was a common problem with 6920s of that era.”