.22 Winchester Magnum Rimfire

Winchester introduced this round in 1959 by lengthening the case of its own obsolete .22 Winchester Rimfire, and it was designed from the start around a jacketed bullet rather than the bare lead every rimfire before it had used. It has been in continuous production since, chambered in rifles, in revolvers and in a handful of self-loading pistols.

What separates it from the .22 Long Rifle is geometry rather than pressure — the two run at nearly the same C.I.P. ceiling. A .22 Long Rifle uses a heeled bullet: the bullet is as wide as the outside of the case and is stepped down at its base to fit into the mouth, so a band of lubricated lead rides exposed into the chamber throat, and that surface is what limits how fast the bullet can be driven before it strips in the rifling. The .22 WMR instead seats a full-diameter bullet inside a wider case, where it can carry a copper jacket and never touches the throat unjacketed. Eleven extra millimetres of case supply the volume, and the jacket is what allows the velocity to be used.

The consequence is that the two rounds are not interchangeable in either direction. A .22 WMR will not enter a .22 Long Rifle chamber, and a .22 Long Rifle dropped into a .22 WMR chamber is unsupported at the case walls. Revolver makers answer this with two cylinders and one frame, sold as a convertible pair.

Because it headspaces on a rim and cannot be reloaded, the round has stayed a factory-only proposition, which is why the load table below is short: the three published weights are 30, 40 and 50 grains, all measured out of the same 24-inch test barrel. The 40-grain load is the original.

Gaps on this page: no manufacturer’s own ballistics sheet was found for these loads, so the velocities come from an encyclopedia table citing Cartridges of the World rather than from a maker. Every figure in the table shares one 24-inch barrel, so there is only a single sourced point per load and no barrel-length curve can be drawn — a .22 WMR out of a revolver is a substantially slower cartridge and this page cannot say by how much. The pressure ceiling recorded here is the C.I.P. one; the SAAMI figure is quoted in the same encyclopedia article but the two bodies do not measure the same way.