The world of magnum calibers and revolvers typically offers you a degree of versatility. Your .357 Magnum can fire the less powerful and often cheaper .38 Special. Your .44 Magnum can fire a .44 Special. When you follow that logic, it seems perfectly safe to toss a .22LR in a .22 Magnum revolver, derringer, or whatever. However, you’d be wrong, and you’d be doing something a fair bit unsafe. Here is the bottom line up front, don’t put a .22LR into a .22 WMR.
Why Not? It Fits
Yeah, it does. The .22LR will drop right in and seems to fit nicely. It certainly won’t argue with your .22 Magnum cylinder, so why can’t I fire .22LR from a .22 Magnum? Price-wise, .22LR is much cheaper than .22 Magnum and much easier to find. It seems like it would be a perfect training round.
The problem comes from how both the projectiles and cases are designed. When Winchester created the .22 WMR, they didn’t just stretch the .22LR round. The .22 WMR uses a case that encloses the full diameter of the bullet.
A .22LR round attaches to a foot connected to the projectile, and this foot is smaller than the overall diameter of the bullet. The case of the .22LR is a bit thinner and smaller than the .22 Magnum.
The case diameter of a .22LR is .2252 inches, and the .22 Magnum is .2421. The rim is thicker, and it’s just bigger in nearly every way. The .22 Mag is a great cartridge, but you can’t drop the .22LR in the same cylinder or chamber and hope it works.
What Will Happen if Your Drop .22LR in a .22 Magnum?
Since the .22 Magnum is larger, the chamber is also larger. Because the .22LR is smaller, it does drop into the .22 WMR cylinder easily enough. However, it fits sloppily inside the cylinder. This leaves extra room and allows the case to rupture and explode inside the cylinder.
When this occurs, debris and gases can be shot backward or out the sides and hurt the shooter. It could also damage your gun beyond repair, and shooting the wrong caliber out of the gun will violate your warranty, so don’t expect a company to fix your mistake. Plus, you might be picking metal out of your face.
How to Shoot .22LR in a .22 Magnum
There is only one safe way to shoot a .22LR out of your .22 Mag. It has to be a revolver, and you have to swap cylinders. Plenty of revolvers allow you to swap cylinders and can be fairly affordable. The Heritage Manufacturing series of revolvers offer quick and easy change cylinders for a fairly low price. Numerous revolvers do the same, and that’s the only safe way you are going to fire .22LR and .22 Magnum from the same gun.
If it’s an automatic derringer, lever action, or any other weapon, it’s simply not safe to drop a .22LR into a .22 WMR weapon. It is simple, but it doesn’t seem to be well understood even to this day. I’ve seen people saying it’s safe, and it’s downright silly to still suggest that a .22LR in a .22 Mag is a safe bet.