Actually, the 22 Mag requires a slightly larger bore diameter than 22 LR. I believe it's .224 vs. .223 or something like that. Anyway, it's enough to cause a problem. Some guns are set up to handle both, such as the Ruger Single Six, but they have the larger bore diameter for the 22 Mag and supposedly the accuracy of the smaller diameter 22 LR bullets suffers because of this.