Guessing... gunpartscorp? Aka Numrichs?
Ahyup!
Yes, GPC = Gun Parts Corp
I seem to buy most of my retail parts from GPC or Jack First, sometimes CDNN when they are closing out the parts, and sometimes guns, that are left after a company, like USRA and Marlin, has been closed down.
The unmarked GPC 99 barrels that I've had and seen have all had dovetails cut for the rear sight, the barrel stud for attaching the forearm, and hole(s) d&t for a ramp front sight. I have never seen a new, verses recycled, after-market barrel on a 99 that was milled or d&t for open sights.
