There are two hard and fast rules in this house concerning AR's. One, the uppers get marked in white paint pen with the chambering, on both sides. Two, magazine segregation. .223/5.56 is put in USGI metal mags only. 300 BLK goes in P-mags. .224 Valkyrie and MSR-10 mags get paint pen'd with chambering.
Attachment 227205