I joined the forum a few weeks ago and just been lurking. I bought a 16 inch Bushmaster Factory 450 about two weeks ago from Walsh. I finally got to test fire it today with Hornady factory ammo. All rounds fired and ejected, however, only the first round locked back the bolt on an empty magazine. I fired 9 rounds total and had 8 that short stroked. All ejected at 2:30-3:00. The upper is assembled with a mil-spec collapsable stock. I figured it may need some break in, so I re-lubed the BCG and hope to re-test in a few days. Is there any thing else I should be looking for?