There was a thread on here by (Musashi?) where he studied it in depth and worked out a method to DIY it that looks pretty good to me. He said the USAMTU does it, I wonder if the USMC variant does it. I never saw one of their rifles disassembled but I do know they build them from "scratch" --they do a little bit more than just assemble them.
Now I can't say much about bedding the rifle, but I can say that accu-wedges were invented for this, we used to use them for SDM's initially. They liked them. The issue lies with the upper and lower's tolerances being too great and allowing motion between the two. However, with a solid sling and cheek, I can't see the use for bedding or for the accu-wedge. I shot the highest score anyone has ever shot in an SDM program (back when it was at Ft. Lewis and was actually a challenge). I did it without the accu-wedge, everyone else had 'em. All our weapons were identical, some actually had better barrels than mine. All issue. Biggest change in groups came from 1. standard adj. stock (not the SOPMOD) vs. an A1 or A2 (I prefer A1's). 2. Free floating the barrel --it takes the pressures off the sling and keeps the groups from shifting. It also tightens up the groups in general even when no pressure is applied. The #1 most important feature to any AR will be the barrel. A solid cut rifle barrel made by a master, and saying it's also one of his "better" ones, will always account for more than 95% (some say 99%, I like to think there are few other variables) of the accuracy in that system.
Accuracy? FF, quality barrel, fixed stock or a solid or a SOPMOD maybe (I actually just started using those since KAC started using them on their M110's and I have to say I'm surprised about using a collapsible on a sniper rifle but this one actually works IMO/E). A Turner sling or the 1985/6 or much earlier models (certain ones are better, you can do the legwork). That and the fundamentals, etc., etc., always made a bigger difference.
I once took a factory OLY rifle, yes a goddam Olympic, and I put a good barrel in it and a KAC FF carbine tube and a decent trigger. This rifle outshot every other one on the line. Now the Oly with the factory parts blew the gas block off and the FF tube came loose and it blew the gas block off downrange. Less than 1000rds., Oly didn't see it prudent to take our advice and unfuck their designs. They didn't want army contracts anyway (though they somehow got to test out the SOPMOD package? WTF?) We stuck with KAC and companies that listened to us.
One thing I did, more out of being anal in construction than anything else, was to match all my parts. I bought a shitload of uppers and I get my lowers a few at a time and I mix and match until I find one that naturally fits very tight. Never had a problem doing this. Doing this with an AR10 may be more costly but I have an answer to that too: Rainier, if you ask nicely, just might go in the back and mix and match uppers for you and make you a match set for free. They're pretty cool people and cater more to the 3gun/comp. guys vs. tactical shit.
I won't be bedding my rifles, but it's because I've gone this long without needing to (can I REALLY get better than .33MOA w/6.5G, or am I just gonna fuck that up?). I won't knock it, I'm okay with overkill, but I WOULD like to see a bedded rifle vs. the exact same rifle minus the bedding. That's the only way to know if it's worth it.
USAMTU keeps very good dope and they know their rifles inside and out. It's possible they get a bit of advantage from this, but I'm not so sure the rest of us have dope or data that accurate, nor do we analyze it mathematically. Then they are also always playing around. We also have a saying, "eliminate as many variables as you can" so it's down to the shooter and skill as much as possible.
Good luck with it, but not sure it's necessary. Oh, and FWIW, my M110 doesn't have any play between the receivers. They've been getting a lot closer over the years I've noticed. All of the major mfg.'s.
