Just happened to me on Sunday. This is a new purchase NIB and I was function testing with dummy rounds at home. All went ok but then when I am done packing up I found a long screw on the table. Immediately I recognize it is the probably the long chassis screw. Sure enough it was. Not a big deal and I screw it back in make sure it is tight enough to now loose again. I can't imagine how it came loose so easily and eventually fell on the table unless the factory just barely put it on with like half a twist. Yet this is one of the two screw basically acts as the anchor for the chassis.