I have an Olympic Arms AR-15, post ban.

I was looking at my bolt carrier... and was looking at the AR15/M16 differences on old.ar15.com.  I noticed my bolt carrier is very similar to a M16 carrier, because it does not have the firing pin area milled away like some AR's to expose the pin collar, and also does not have much of the sear trip area milled.... looks to be about a quarter inch removed.

Basically, this looks very much like a M16 carrier that was modified to be legal for AR.  It even has an area near the carrier key that you can tell was stamped "FN" but it is ground out to make it barely legible.

Does Olympic use military contract Bolt Carrier's, and just mill the sear trip area and use them in their AR15's?

I don't really know but I am venturing a guess that manufacturers like Oly & Bushmaster etc buy them from whoever is the cheapest or available.  I read somewhere on these boards that FN USA is prohibited from making any guns for the commercial(civilian) market, rather than scraping a bunch of bolt carriers and losing the labor and materials, they just make it legal for the civilan market.