Magazine conversions always seem to be an issue with folks who dislike the AR10, usually it's coming from the crowd who wished that the design used cheap FAL magazines or a dedicated magazine like the SR25s. In the end, I really like having a gun that shares it's magazines with the M14, I plan on owning an M1A some day and having magazines that will work in either gun is a benefit to me. If converted in the right way, the M14 magazine tubes can need only so little as the slot milled into the magazine well in the correct location. If the lug is left on the back of the magazine, it will retain full function as an M14 magazine while only losing the "bolt hold open" feature that comes with the modified follower of the AR10 magazine conversion.
In short, an M14 magazine with the slot milled in the side and using the polymer AR10 follower would work in both rifles with the exception of neither rifle having a last shot bolt hold open.
It's also possible to grab an unconverted M14 magazine and fire it from an AR10 if you absolutely had to, you have to hold it in place while shooting but it is possible. The AR10 upper receiver has a sort of ledge built into it that appears to prevent over insertion of a magazine.
My 20 inch AR10 A4 with chrome lined barrrel, with better handloads it gets under 1 inch for 5 shots at 100 yards while fighting the long heavy trigger pull.
I'm waiting on funds to order off a 2nd upper assembly in it in 260Remington, want to try to get it into an accurized long range configuration. Probably going to be looking into the Nightforce line of scopes to go along with it as well.
Edited to add, Armalite customer service is the best of all companies out there who make AR style 308s. I've had to deal with them in the past for customer service and it's been the best experience I've ever had in dealing with a firearms company, helpfull and friendly to say the least. Only thing that prevents me from buying more Armalite rifles? Living in Ca., but maybe I'll get an AR50 one of these days
Knights is reknowned for being overly concerned with government business contracts and satisfying the civilians 2nd to gov't. contracts. Good product but high price and not the best of customer relations.
ASA has the misfortune of having one of the worst reputations going, generally their word is not to be trusted. Hesse is likely the only ones to rank lower. ASA and Hesse, worst product consistency out there by far and often times have reports of the worst customer service imaginable.
Supposedly DPMS is coming out with a target AR 308 configuration, won't be a high capacity capable critter though by the sounds of it(buzz was on AR15.com forums a month or two ago).