its suggested around here not to use UMC. Ive used more than 1k roudns of wolf and brown bear(mostly brown bear) withought issue. I bought 3 boxes of UMC and had my first malfunction 2 days ago. Because of the reputation i checked all the rounds(twisted the bullet with my fingers) and all seemed firm, but when shooting, i had a FTF. pulled the actionp back and saw an "empty" sitting on top of the mag. after pulling it out, i saw that the bullet had pushed nealy all the way into the casing. The bullet is sticking out 3/16ths of an inch. the edge of the casing caught the feed ramps and stuck. When playing with it it fed. Had it fed whilst shooting i could have had a blown up gun. Needless to say i will not be using umc anymore(unless i get a bolt gun). Just thought id share another tally...
I highly recomend not using this stuff in your ar, better off with steel.
edit - oops, sorry for wrong forum, mods