Picked up my first AR a couple weeks ago. Private sale, got 6 mags and about 600 rounds of .223 ammo.
It shoots .223 fine. But am curious about 5.56x45
No barrel markings anywhere except "C MP C" stamps the underside between the front sight and the flash suppressor.
I'm 95% sure that the upper is completely Colt (model 602 I think) - but without a marking on the barrel to tell, how to know which caliber?
ETA: no markings under handguard either