maico75, I'm having same problem. Just shot my 10 today... ACS mag piece of sh*t! 1st round loads, but then the remaining rounds all seem to move forward in the mag (out of position) and bam*** no worky.. initial feeding ok, seems to run 1st 3-4 rounds then bam*** no worky... Thought maybe I didn't load mag properly so unload, reload start and bam*** no worky - SH*T...Just picked up my new M&P 10 saturday. Same problem with not feeding with the stock magazine. The first round will chamber and fire but the next round will not move up all the way to the lips in the rear of the mag and the bolt will not strip it off to chamber. Usually it will just push it back in to the magazine but sometimes will try to chamber it and bend the cartidge. Tried a Magpul PMAG and it worked fine. It seems to be a follower problem. Tried Frog lube and it did not improve. S&W told me to send the mag back and they will fix it.
After multiple attempts, I noticed the follower was not flush. I think this is a mag issue, not an ammo issue. No problem with eject.
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