Well, I'm a bit disappointed. The big M&P-10 Sport didn't want to cooperate with me last night. Field-stripped and cleaned (not an extreme, thorough cleaning, I admit, because it wasn't dirty - just got most of the preservative oil off, that was on it). The patch I ran through the barrel did come out with some carbon, so, I reckon they test-fired it before leaving the factory. Lubed with synthetic motor oil (I think it was some Pennzoil Platinum 10W-30 I had left over from the car - I honestly can't remember, because I keep it in a syringe. The only other thing it could be is the M1-EP 5W-30 I use in the truck. Anyway, I thought I'd lubed it pretty generously. More on that later... Got to the range, put the scope on, and started shooting with some Federal XM80C (Lake City 149g, 7.62x51mm). It was grouping well at 25 yards - definitely under 2" - then it jammed. What it did to the case of the cartridge. It also set the bullet back in the case a hair. Had to remove mag to clear the jam. Got it cleared, chambered another round, fired, pulled trigger again, CLICK. Removed mag and looked. Bolt had failed to strip a fresh round from the magazine. And I could see score marks across the top of the cartridge case, where, presumably, the bolt rode over top of the round and scratched it: It did this kind of thing a few more times, and, once, I couldn't even pull the charging handle back without removing the mag and pulling really hard. So, I decided to take it upstairs and let one of the old guys who works there look at it. We field-stripped it and he said everything looked OK, but that maybe it needed more lube. He handed me some CLP called "Clenzoil", I think (it was pretty thin stuff). We lubed everything generously. Took it back down to the range and tried again with some different ammo - this time, Aguila 150g 7.62x51mm. Same problems. FTFs. At this point I didn't want to mess with it anymore, so I got my Dan Wesson Heritage 1911 out. That saved my range trip - I love that pistol. Never a single malfuction. Right now, the plan is to clean and lube again, even though it's pretty wet at the moment and only has about 15 rounds, or less, through it, and see if I can get my hands on a couple of different magazines to try. I also have a box of Federal .308 180g hunting rounds. Those should be a little hotter than that milsurp 7.62 stuff. So I'll try that. But, IMO, this thing should handle 7.62 NATO stuff just fine. I'm also going to call Smith & Wesson tomorrow and let them know what happened and see if they've been hearing of this kind of thing, with these rifles, because I know they've sold a bunch of them. Also going to ask them if they'll send me a different mag. It came with one 20-round PMAG. Those are usually GTG, so, I dunno. I haven't had a single malfunction with my Colt 6920. But, then, it's a different animal. Any ideas?