AR-180B-2 Barrel Extension / Trunnion issue

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SIIaCanuck

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I just received a 'new to me' AR-180B-2 (the non-restricted version).

When I chambered and ejected a round to check function, the bullet came out scored like this:



When I inspected the trunnion, I found a burr of metal coming off the RHS of the extension lug between the feed ramps and smaller one off the RHS of the lug left of the left feed ramp.

Here's a photo:



I surmise that the bolt opening while chamber pressure is still excessive could explain the wear that would produce this, but I'd like other opinions. Could the extension be slightly out of tune with the bolt group (rotated slightly)? You can see wear on the remaining lugs on the same side, no burr off the locking face, but on the side of the lug.

Bolt shows no sign of wear/damage.

I'm also going to take the rifle to a gunsmith to have it looked over, but I am concerned that I'm going to have to remove the barrel, press out the barrel extension, and put in another one. Not a difficult job, but not a quick 30 min job either and I was hoping to be out shooting!

Thoughts?

Stew
 
I had a similar problem with one I owned (my second one)
I just hit it with a rat tail file slowly to remove the burr and polish the ramps.
No more problems. No more etched projectiles.
Funny that's exactly how I noticed mine. I unloaded and when I picked up the round I noticed a long gouge in the side of my ejected projectile.
You will not have to remove the barrel. It's just a burr from the machining process. File it off lightly with a rat tail file. Or if you don't trust your hand, get a gunsmith to charge you $120 for the 5 minutes of work.
 
File off burr, go shoot your gun. Problem solved.

Let us know if it continues to be an issue and then we can go from there. With no wear on the bolt, you should be good to go just removing the burr.
 
You can see the copper covered burr on the right side of the bottom abutment. Look at the same area on the next one to the left. Does it appear to have a slight lip? I wonder if there is some peening going on.
 
Thanks all. On closer inspection, the burrs seem to be remnants of the machining of the feed ramps. The tooling for both ramps obviously cut the same direction, hence the burr occurring on the right side of the ramp where the tool finished it's cut. The cycling of the action, primarily on opening, curled each burr and made it look, at first glance, as though there was some peening occurring.

I took off the burrs and polished the ramps with some fine grit sandpaper rolled onto a small dowel. With the burrs removed, the forward face of the lugs show no other sign of unusual wear, which should be apparent if peening caused the issue.

So. .

Checked function . . . great.

Test fire . . . all is well.
 
SIIaCanuck said:
Thanks all. On closer inspection, the burrs seem to be remnants of the machining of the feed ramps. The tooling for both ramps obviously cut the same direction, hence the burr occurring on the right side of the ramp where the tool finished it's cut. The cycling of the action, primarily on opening, curled each burr and made it look, at first glance, as though there was some peening occurring.

I took off the burrs and polished the ramps with some fine grit sandpaper rolled onto a small dowel. With the burrs removed, the forward face of the lugs show no other sign of unusual wear, which should be apparent if peening caused the issue.

So. .

Checked function . . . great.

Test fire . . . all is well.
Click to expand...

There you go!
AR180 is a great gun. Just wish they would revive it again and start having critical parts support.
 
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