AR-180B "tinkering"

cyclone

cyclone

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Has anyone here ever attempted a "lug" like the one described on this site (come to think of it, I have strong suppositions it may have bee a CGN member!):


http://coyoteschool.########.ca/2012/10/ar-180b-review.html



Even before buying the rifle, I’d read many internet stories about these guns having a weak spot at the hinge. As if to reinforce this, the factory manual on the rifle makes a big deal out of not overstressing the hinge by opening the gun up too “wide.” That made sense to me when I first read it and I was always paranoid about it while working with the gun, even to the extent of never letting anyone else crack it open. Therefore, I knew that wasn’t the problem. So, what caused the breakage? I started to think about recoil, but discounted that theory with the realization those forces all drive back into the body of the lower and don’t stress the hinge at all. Then, the light came on.

It wasn’t opening the gun too wide, or the recoil that was breaking the hinge; it was feeding and going into battery. After all, the bolt and carrier assembly weigh close to one pound and get slammed forward by two stout springs every time the gun cycles. All of those forces are doing their best to drive the upper off the lower and the only thing stopping that from happening are two 0.10-inch thick pieces of polymer at the hinge. I tried to think of a way to reinforce the hinge, but came up empty.

That’s when I started to consider using a lug instead of the hinge to absorb the return-to-battery forces. Think of a recoil lug that’s really a return-to-battery lug. And there just happens to be a perfect spot for one at the rear of the upper receiver, with a matching recess in the lower just above the pistol grip.

I found a suitable piece of aluminum and whittled out a functional T-shaped lug.

I located the right position for it by wrapping the lug with masking tape until it was a snug fit in the lower’s recess. Then, a light coating of lipstick on top of the lug and a gentle pressing together of the rifle’s two halves showed me where to drill and tap the upper. I mounted the lug with screws secured by removable Loctite® and ensured they didn’t interfere with carrier travel. Then it was a simple matter of applying Acraglas® bedding compound to the lug’s seat for a perfect fit. I added black dye, and as you can see in the accompanying photo, it looks like the rifle was built that way.

After the Acraglas® set and I’d cleaned up the job, I found the fit between upper and lower was a little too tight. A few strokes with a fine-cut file lowered the Acraglas® at the lug seat enough for the upper to lock into the lower with just a gentle squeeze. Any slop between upper and lower was now gone and when assembled, the rifle felt like a single unit.

I gave the bedding compound a week to harden and then took off for the range............
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Interesting! But have some of the reported breakages happened during firing or only when opening the halves and letting them drop open too hard. Been a while since I've looked at AR 180 failures. If I remember right there is only 1 instance of breakage during firing but as always I can be mistaken. Still might be worth looking into.
 
crashcollins said:
Interesting! But have some of the reported breakages happened during firing or only when opening the halves and letting them drop open too hard. Been a while since I've looked at AR 180 failures. If I remember right there is only 1 instance of breakage during firing but as always I can be mistaken. Still might be worth looking into.
Click to expand...


Thanks for the follow-up!
 
It took 3 for me to get a good one .
Bought 1st new from the importer
Fired aprox 60 rnds , lower broke .
Sent it back . Got replacement
Fired 300 rnds lower broke .
Sent it back . Got replacement .
Fired 500 rnds lower did not break .
Importer told me Armalite had a bad batch of lowers.
3rd one seemed good so never fired it again (just in case )
Sold it & new owner never had an issue as far as I know
 
Other than the bad batch that had problems I don't think any have ever broke while firing, only when someone opens it and let's the upper swing down and slam against the lower.
I wouldn't worry about it, not worth messing with the rifle. It's a good design and it's strong enough if you are careful when opening it to clean it. Even an AR would eventually break if you let it swing open and slam the lower.
 
Wish I never sold mine. Now like hens teeth to buy one. I had a nutter turn the integral muzzle brake down and have it threaded for 1/2-28 and wouldn't even know.
 
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