Test barrel length: carbine (higher velocity) and 5.0" pistol
22 TCM case details
The .22 TCM or 22TCM (.22 Tuason Craig Micromagnum) is a proprietary bottle-necked cartridge created from a 5.56 nato cartridge developed by custom gunsmith Fred Craig and Rock Island Armory (RIA) for semi-automatic pistols and the Rock Island M22 TCM bolt action rifle. Before the cartridge was commercialized, it was called the 22 Micro-Mag. Similar conceptually to other bottle-necked pistol cartridges such as the larger-caliber .357 SIG, the .22 TCM trades bullet mass for increased velocity and lowered recoil.
Based on the 5.56×45mm NATO case and shortened so that the shoulder is at approximately the same length as a .38 Super cartridge, the .22 TCM is somewhat longer than the ubiquitous 9×19mm Parabellum and designed to be fired from a RIA line of weapons (which also included 9mm barrel swaps) fed by Para-Ordnance-style double-column .38 Super magazines. A sub-variant, the 22 TCM 9R, with a shorter, more deeply-seated bullet, is designed for use in Glock magazines limited to standard-length 9mm cartridges. Standard factory loads are 40-grain jacketed soft hollow point, 39-grain for "9R".
The .22 TCM 9R (right) uses a shorter bullet than the regular round (left).