Hmmm.... They might have replaced a part or 2 INSIDE the gun because you can see all the original, I think, stamped serial numbers match. I'm gonna try to disassemble it as far as I can to be sure. Can't clean it up yet because I'm going to use minneral spirits. My garage is disconnected and it's dang cold outside so all I can do right now is "play" with it and get familar with how it comes apart/together.
*EDIT*
Disassembled the entire gun. All stamped serial numbers match. Probably replaced the firing pin, spring, or gas piston.
OK, yer right Dale. It was a fixed gun. One place on the barrel itself I didn't see before and found the ONLY part that was replaced on the gun. Because of that 1 part they changed the serial number for the whole gun.
Thanks for the help!