AR 15 300 Whisper Not Cycling/Ejecting

[milehipo]

I want to thank all for the help and different posts. As stated I was using PMags. I took one apart and used my dremel to trim specified areas. The rifle cycles properly and loads and ejexts rounds as it should.
Now my issues are with groups. As stated earilier I am using 9.1 gr. of H110. Groups are 3-4 inches at best. Tried 9.6 of same powder and groups did not improve much.
Is it that I need to allow the barrel to break in?
All components are tight(Optics, suppressor).
Thanks for the help.