Dimensions and loading[edit]

The .22 WMR uses a larger case than the more popular .22 Long Rifle (LR) both in diameter and length. The .22 WMR case is a lengthened version of the older .22 WRF. In the most common modern .22 WMR loadings using a 40-grain (2.6 g) bullet, the combination of more powder and higher sustained pressures gives velocities of 1,875 feet per second (572 m/s) from a rifle and 1,500 feet per second (460 m/s) from a handgun. Because of its larger size, a .22 WMR round will not fit into the chamber of a .22 LR firearm.

Although the bullet diameters are the same, the larger .22 WMR chamber does not support the smaller .22 LR cartridge. Firing the smaller .22 LR round in a .22 WMR chamber results in swollen or split cartridge cases, high pressure gas leakage from the rear of the chamber, and bullets striking the chamber throat out of alignment, which can result in injury to the shooter or bystander and which does result in poor ammunition performance.

Gun makers offer .22 revolver models with cylinders chambered either in .22 LR or in .22 WMR and as convertible kits with both cylinders which allow the shooter to easily switch calibers on the same firearm.