I picked up a new ar180b on Sunday, cost me $690 + tax, $40 over list :(

Well I went to the range today and got a chance to break it in.. :) Everything was working fine till I'd get to the last round in the mag. Every last round, no matter which mag I used failed to feed. Apparently, the bolt would just miss the round and close on an empty chamber. No matter what I tried I got the same results, fail to feed on the last round. I don't see how more breaking in might cure this problem, only thing I can imagine fixing this is the rifle taking a trip back to armalite. Other then that there were no other issues. Recoil was very light, I didn't adjust the sights but.. shooting at paint can lids at 100 yds resulted in mostly hits. I was just function testing the weapon and trying to break in the barrel. If it weren't for the last round fail to feeds this gun would be a winner. I'd hope armalite can solve this issue....

Were the mags the same manufacturer? How fresh are the springs in the mags?

Maybe the gun needed some lube ?

Mags were colt 20's and mostly new usgi 30's. The gun was well lubed. Working the action, you could see the bolt pass over the last round in the mag, it would just miss the rear of the cartridge. Instead of picking it up like all the rounds before it.

BuLLet, I see you are using new USGI 30's and still having problems. Have you tried these mags in another weapon? It still sounds like a mag prob. They may have a follower prob, weak spring or they are not seated all the way in the mag well. It is possible but not likely that the bolt catch itself is sticking or has a weak spring. If you can remove the bolt catch and clean/lube the area that it sits in. If no good call Armalite tech support.

The mag catch of course sits in plastic, and it does lock up solidly when a mag is inserted. Everyone of these mags work fine in other weapons. The bolt locks open on an empty mag every time, though, of course, only if I insert an empty mag to check it. As it won't do this during firing, because it won't strip that last round off.

Bullet-
  Had this same problem with my 180B.  It's definetly mag springs, I broke out a couple NIW mags and they work perfectly.  Jeff

Hmm.. ok, the mags are a few years old but, they were practically unused, like new. I do have some 91/92 niw usgi's I can try. But, the mags I did try were working fine in my colts, and bushies. I have some new unused thermolds I could try as well.

Doug, I still suspect the mags. I would definetly open up a newer mag or get a mag rebuild kit with springs and green followers and give it a run. I had a few NIW USGI mags go bad with no apparent reason, in fact I think it was you who squeezed the lips together on my new 30rd mag at the first L.I. shoot. That mag was one that I had since first issue and I opened it about a month prior to the shoot and it had problems the first day out. I had another one that did the same thing as your AR180, but only in my AR15, when used in my buddies AR180 it locked the bolt! So it is possible for the mags to function in an AR15 and not in an AR180 and vice a verse.

I just took another look at it, put a brand new usgi (92) in and cycled the rifle with no rounds in it. It locked open like it should, I loaded up some dummy 223 rounds, no primer or powder, and tried feeding those. With the bolt locked open I inserted the usgi mag with one round in it, as soon as the mag was inserted the bolt shot forward and it stripped off that round. I tried it a few more times and some times it would strip, some times not. I also put 3 rounds in one time and it wouldn't take any of those, went right over them. I then tried another 20 round colt, 100% unused mag. It would not strip the last round. I looked more closely at how the mag was sitting in the well, it's fully seated as it should be.. but, I did notice that the bolt catch is pushing the rear of the round down some, so that it's no longer being held tightly against the mag lip. This appears to be the problem, I think. :) That bolt catch is also larger then my colt's or bushmaster's. Maybe it's spring is just a tad too strong, I don't know for sure.. but, some more testing needs to be done..

The AR180 is tough weapon, that's why the IRA favors them. It might just be a case of a very tough weapon that needs to break in. I guess we can rule out the mags by now. Did you lube up the guide rods, if not you should make sure they are properly lubed, this will probably remedy part of your problem, FTF. Any word from Armalite?

The guiderods were dripping from oil, it seemed well lubed from the factory. I can clean off what they used and put something of my own on, something better then what comes from the factory. And, no word from armalite as of yet, I'm sure they are not reading posts here on the weekend.. :)

So your bolt catch is a hair long?  That makes sense.  Try stoning the tip of the bolt catch back a bit and that should clear it if you're right.  Mine definitely sticks forward farther than the ones on my 15s do but it works fine.