Thanks for the rundown, I am looking forward to what Alex has up his sleeve
If your not happy with it...dump it now on gunbroker or e-bay while they are bringing top dollar. Some guy is selling them for $370 right now on ebay and getting it.I've gotten more time to fool around with the UBR/XCR combo today.
I think one thing I'm running into is that the XCR really doesn't interface all that well with AR15 accessories. Things designed for the AR boreline just don't line up quite right with the XCR. It's not far off, but there is a difference. I think low mount bases are a must right now. I have Larue high mounts presently installed (typical AR15 height). They're just a touch too high. Same with the KAC irons. This isn't a huge deal, but it's noticeable. With the FAL folder you don't really have a cheek weld like you do with more substantial stocks. I know I index the stock from the flat bone just behind the chin. This gives you a headsup position that lines up fairly well with the AR15 stuff.
Queue up the UBR. The UBR has a very substantial flat where your cheekweld will be. It's very comfortable, but promotes a lowered head in relation to the sights. You can adjust your cheekweld so everything lines up OK, but it really could use about 3/8" more height. The cheekpiece of the UBR is removable and replaceable with different heights, widths, etc. However, Magpul isn't even making the stocks for commercial sales just yet, much less replacement cheekpieces. Advice is to get as low as you can go for mounts on the XCR. Anyone thinking about going Larue, I'd recomend the 1.4" mounts (think that's what they are; it's on the site).
Then there's LOP. There's no way around having an excessive LOP with the folding M4 block. I'm not sure exactly what I'm going to do with mine at this point. I suppose I'll leave it as it presently is for a few weeks and see how it grows (or not) on me. I'm thinking about getting a fixed M4 block, however. The protrusion that doesn't allow the stock to fully collapse (about 1/8" gap) is an index detent that normally would be inside the AR15s reciever. On the XCR it just butts up against the block. This could be ground off, but I'm not sure I'll keep the stock at this point so I'm not too inclined to go hacking on it just yet.
If Alex does bring out a SCAR-style fishtail stock for the XCR, I'll be first in line with cash. The UBR is OK, but it's not THE stock for the XCR. We don't have that stock yet. I think the gun does need a stock that brings the cheekpiece all the way to the top of the reciever because of the heights of existing mounting hardware. A fishtail style stock with the hinge flush against the reciever would solve the height issues, I'm thinking. Also, we wouldn't have to put up with a buffer tube we don't need.