Just put a new upper together. 13.7 stainless mid gas barrel, kit came with a bcg & gas block/tube. Using a H buffer & carbine spring. Went to do a quick zero, locked bolt back, inserted mag, hit bolt release, round did not fully chamber. Pulled out mag, round then chambered completely. Fired mag until empty & got lock back, put in fresh mag, hit the bolt release & the same sequence happened. Ammo was steel case brown bear. Mags were usgi loaded to 28 rounds. This happened with & without a suppressor on. Any thoughts? Thank you