Hi Folks, I picked up a second hand M4 at a legit dealer and am having some confusion that the serial number by the trigger guard and the one on the barrel do not match! The date codes are the same (CM). Receiver serial is Y079***D14 Barrel is TM84***D14. Gun is in great shape operates fantastic. Thinking somebody bulged the barrel or a police dept. accidently swapped parts or made one good gun out of two bad ones. Any thoughts? Thanks.