I just recently purchased a new 16" upper, factory built, from a company at the upper end of the "mid tier" of AR rifles. After the first ~25 rounds (PMC Bronze .223), I opened it up to run a boresnake through and as I separated the lower from the upper, I noticed two small parts skittering across the table (items in the center and right side of the photo). I wasn't able to readily ID them as parts I recognized, and I wasn't sure if they were from my rifle or just loose junk on the table. An inspection of the rifle by me and one of the range staff didn't reveal anything noticeably amiss, so I shot another 20-30 rounds and everything felt/heard/looked fine. End of range session.
When I got home, I racked the handle to do a brass check before putting it away in the safe, and a small piece of roller pin (left side of photo) fell out of the ejection part. So loose parts are definitely coming out of this gun. However, I can't tell if something is broken internally, or it's some junk left over from the manufacturing/packing process. Nothing in the gun (bolt, carrier, extractor, trigger group, mag release, etc) looks broken or appears out of spec to my well-read but admittedly amateur eye.
Lower is a home-assembled receiver with an Ace stock and LWRCi Enhanced LPK which has provided at least 1500-2000 rounds of flawless performance with a variety of Colt and BCM uppers.
Does anyone know what these parts are?