I've got an LMG upper and yes, it will run fine with a standard rifle buffer (though not with a carbine buffer; it will, however, run with the Vltor A5 buffer and tube). I recently picked up NOS COLT LMG hydraulic buffer and green spring on gun broker for under $200, so they do surface from time to time.

The LMG is actually a lot of fun, though heavy as all get-out with a loaded Betamag. It's fun to shoot sitting and just walk the rounds onto the target. As noted above, you can make replacement HD gas tubes for it.

I was one of the 2001 Shrike depositors and finally got mine with it started shipping, but when I shot it for awhile, it just didn't do it for me. I also had concerns about wear on my factory Colt M16A1, so eventually I sold the Shrike.

Right now I have about 15 uppers in 5.56. Every time I go to the range, I take along three to five uppers. If I'm doing mag dumps, I swap uppers every two or three 30-round mags, so there is always one cool enough to shoot. In 50k rounds, I've never melted a gas tube with this system.

My favorite barrel length is 14.5" -- it just handles right to me -- and awhile back, I picked up a bunch of used LE-takeoff Colt M4A2 and M4A3 14.5" uppers for $350 each including CH and BCG. The bores were VG+ and they shoot fine, no tumbling yet, so I just rotate through them at the range.

YMMV. Hope this helps.

Dennis Todd or SAW might have one, but otherwise the auctions sites are it.

Colt only brought in one batch of these from the Diemaco facility in Canada, at least 20 years ago, for a potential military contract. When it did not happen, they added semi BCGs and sold them though their usual distributors for, IIRC, $799. Today, of course, they are unimportable (unless you want a sliced-and-diced barrel).

The going rate seems to be around $2.5k. There are two on GB right now around that price.

Also, I just checked your original post and see you have an Oly/PAWS. FWIW, I bought one of those from a local friend shortly before I got my ARES Shrike, with the idea of making it the primary host for my incoming beltfed upper. Even though the Oly/PAWS ran perfectly with every other upper I own (including the LMG), it simply would not fit the Shrike. It was a stacked tolerances issue. The Oly/PAWS had already been professionally brought into spec once, and I did not want to redo it; and I really did not want to start filing on a $4k upper.

After trying the Shrike on other hosts, I decided I could live without it, and separately sold both the Shrike and the Oly/PAWS (the RR for $4k more than I had paid it less than a year earlier).

Anyway, I do not know if the manufacturer has addressed that issue, so if you do decide to go for an MCR, see if you can find one to test-fit to your RR before you plunk down the cash.

Your Mileage May Vary.

When a previous owner bought it, it would only fit the original Oly upper. He carefully filed down the top deck of the receiver a slight bit, but there was still an issue with the takedown pins: The front one was drilled slightly too far to the rear. It didn't help that the crappy original takedown pins were slightly oversize, and squared off at the leading edge.

I partially solved that for him by taking a new set of Colt mil spec takedown pins and test-fitting them. The were better, but still not enough, so I removed and beveled the leading edges of the Colt pins, and reinstalled them. That worked fine for all his uppers and for my Colt uppers: Sometimes for some uppers you had to tap the pins into place, and out of place, with a little brass hammer, but it worked and was a very nice, tight lockup.

My early (IIRC, 2nd-gen) Shrike was just slightly too long between the TD pin holes. Put in the front pin, and it wouldn't close; put in the rear pin first and you could see how misaligned the front TD pin hole was.

I'm sure M60joe could have welded up/redrilled/installed bushings that would fix it permanently. But by then I had also had some trigger time with my Shrike on another host, and it just didn't do it for me. With short barrels, it did not balance the way my M4 uppers did; with long barrels, I still preferred the accuracy of my LMG. Plus I was able to get my money back through resale of the Shrike and of the Old/PAWS.

In defense of Olympic, they were building semi AR15s at a price point significantly below Colt. That meant looser quality control to keep costs down, and it didn't matter that the factory staff might have to try a couple of uppers when assembling them.

Remember that when the hosts were made in the early 1980's, there was no huge aftermarket of AR15 Barbie Doll accessories. Extra uppers were just not out there, so 95% of AR15 owners only had the upper that came with their rifle, and they were just fine with that.

And then Al Gore invented the internet, and the rest is history....