Caleb is beating the holy hell out of an M&P-15 with the factory low-end MagPul accessory package. (And by "low-end", I mean "de-contented"; the MOE parts I've examined seem to be just as sturdy, just with fewer features. The stock, for instance, lacks the locking feature that makes the CTR stock so solid, and the pistol grip doesn't have the modular front- and backstraps of the MIAD.)
I'm waiting to hear how the MagPul BUPS (Back-Up Plastic Sights) hold up. Do they hold zero with normal handling? Are they rugged enough to take a spill? (Not even all BUIS systems will do that.) I'm skeptical. Perhaps he could accidentally-on-purpose drop the carbine on them?