Lyman MSR Ammo Checkers are for checking your ammo to make sure it will chamber smoothly. It's machined from solid blocks of 6061-T6 aircraft grade aluminum, cut with custom tooling to minimum chamber dimensions and has a black anodized finish. It covers 223/5.56, 6.5 Grendel, 6.8 Rem. SPC,7.62x39, 300AAC Blackout, 450 Bushmaster, 458SOCOM and 50 Beowulf.