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This may help.
I found that when working up loads for my AR 300 that with the 150 gr bullets loaded with 18 gr of H110 was way too hot. They would not extract. Had to knock it out with a cleaning rod. This load really did a job on the primers. Had to go down to 16.8 gr with 150's. These produced 2016 fps (avg) with very good accuracy. All my loads are using .223 Rem brass, Rem primers and trimmed to 1.350.
On the subsonic side, I have good luck using 10.8 gr of AA1680 with the 220 gr Sierra MK's. This load yielded an avg. of 1055 fps with outstanding accuracy and functioning with and without suppressor. I have 100% functioning with both of these loads in semi and FA.
Although a brand new AR rifle/pistol will improve with some breaking in, I don't think this is your problem at this point. Another thing to check is to be sure the gas port in the barrel is at least .125. There is no need for it to be any larger since most gas tubes are no larger than .125 I.D. One other point regarding gas flow, be sure that the gas block and the gas port are perfectly aligned with each other, as is obvious, misalignment will restrict gas flow that can cause weak pressure for the operating system to work properly. But with the load you stated, overpressure in the chamber could likely be your problem.
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