Standard small rifle primers are designed for lower pressure cartridges like the 22 hornet, 222 Rem, or the 218 bee. They have thinner cups. The 223 Rem, 221 Fireball and the 204 Ruger should use either small rifle magnum, military style or better yet, bench rest primers, these all have the thicker cups designed for the higher pressures of these more modern cartridges. The standard small rifle will work, but if your pushing for a max velocity load try the bench rest primers.