I recently tried Wolf's "polymer" coated mat'l and find it works well in my family's AR's. No runs, no hits, no errors of any kind in nearly 2K rds now. It sells for $95-99 per thousand rds at the "fun shows" here in Oregon. I've heard a lot of purists complain about Wolf .223 fuel but the gravel can't tell the difference and the cost savings are significant while accuracy is more than good enough for practice ammo. I can't detect any residual accummulation or wear in the chamber. If it proves to be more abrasive after a few tens of thosuand rds than brass cased ammo, fine, I'll take 1/4 of the savings in ammo costs and rebarrel the upper. I've never used the older lacquer coated cases except in an AK. At 6 to 8 cents per rnd savings over other surplus mat'l, the cost ads up pretty quickly if you shoot alot. Even using surplus costs as 160/K, that's .06 x 30 = $1.80 per 30-rd magazine. I have teen-aged sons that know how to fill magazines and they aren't bashful about emptying them. If cost is an issue, I'd suggest you might want to try some.
PS: Folks who say there are no good reasons to have mag-fed semiauto rifles have obviously never been out with us.... I would trust my sons with my life, literally!! If the anti's can't, don't, or won't either control or trust their children, they shouldn't heap their failures at my feet. (or hopefully, "our" feet, since I hope I'm not alone in this position.) Best of luck!