Just finished assembling a new AR .223/5.56 upper.
Slick sided Upper
16" medium weight SS 1:8 barrel
Ultra thin 14" keymod
ACC quick mount on the end.
I purchased a complete bolt carrier group from a company I do lots of business with (I'm not naming them). Because I'm a little OCD, I break down and clean everything... Including the bolt.
I noticed that the firing pin did not fall out on its own. It took just a nudge from my fingernail, and I just attributed it to being new and being completely dry. What I found next made me me very glad that I didn't just spray some Rem Oil on it and slap in in the rifle.
The two big metal cuttings fell out when I removed the extractor. They are metallic and completely covered with the same phosphated finish as the bolt.
The smallest, at the tip of the firing pin, is donut shaped and was jammed in behind the firing pin hole, and the firing pin would slide through the donut hole.
When assembled, the firing pin would drop in normally, but was only flush with the bolt face...it did not protrude at all from the firing pin hole.
I'm not sure if a hammer strike would have driven it out far enough to ignite a primer, but if it did, it is very likely the pin would be stuck in that position, resulting in a slam fire or an out of battery detonation when the next round chambered.
I've sent an email to the manufacture and suggested they tighten up on QA
(My apologies for the picture being upside down...its that goofy iPhone thing.)