If we are talking a revolver here, then YES. OM stands for original black powder model I assume. The ones made for the army were originally loaded with 45 colt, but the army quickly found out that 45 Schofeld would be cheaper to load and so they were issued as standard ammo later on after Custer I believe. I just bought 500 rounds of 45 Schofeld to shoot in matches. Regards. Deadeye.