Don't think you can interchange the two. The HMR is based on the 22 MAG cartridge casing, the Mach 2 is based on the 22 LR case. The magnum case is larger in diamter than the LR case. Like trying to swap 22 Mag and 22 LR. There ARE revolvers with swappable cylinders, but as far as shooting one cartridge in a gun marked for the other- No.