A1 vs A2, A2 has finer windage adjustment and elevation adjustment the A1 didn’t have, you’d just zero the A1 at 300yds for a combat zero, like a BUIS.
The markings should be on the barrel, right in front of the front sight post, a couple on the upper behind and maybe in front of the ejection port, and possibly one on the bolt carrier.
If it’s Colt, the barrel should have something like MP C 5.56 1/9 on it, and the reciever may have a little keyhole and a “C” behind the ejection port and in front of the port, you may have a “C” inside a square and a little triangle proof mark.
The markings should be on the barrel, right in front of the front sight post, a couple on the upper behind and maybe in front of the ejection port, and possibly one on the bolt carrier.
If it’s Colt, the barrel should have something like MP C 5.56 1/9 on it, and the reciever may have a little keyhole and a “C” behind the ejection port and in front of the port, you may have a “C” inside a square and a little triangle proof mark.
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