RCBS Single Stage shell holders are built from hardened steel and designed to properly align the case with the reloading die in single-stage and turret presses. They're sized to fit specific case heads and capture 0.125 inch of the case head for proper SAAMI headspacing. This model is compatible with the following calibers: 17/222/223(5.56) Rem; 17/221 Rem Fireball; 204 Ruger; 22 Nosler; 6mmx45; 7mm T/C Ugalde; 300 Blackout; 380 ACP; 9mmx18 Ultra.