Ask Foghorn: Can you Fire .22LR Ammunition Through a .22 WMR Chamber?

Brice asks:

Why does a revolver need a .22 and .22 mag cylinder?  The Ruger Single Six, Taurus Tracker, etc all come with two cylinders.  Why?

Short answer is because otherwise the thing might explode. Here’s the long answer:

Two cartridges: .22 Long Rifle (LR) and .22 Winchester Magnum Rifle (WMR) (picture courtesy Wikipedia). On first glance these two cartridges appear almost identical in diameter, and all you would need to fire the WMR out of a LR chamber is to make it a little longer. But looks can be deceiving.

Let’s check out the technical specs of each of these cartridges (in inches):

Case Length.6131.055

Metric .22LR .22WMR
Bullet Diameter .222 .224
Neck Diameter .226 .242
Case Length .613 1.055
Rim Diameter .278 .294

You can see that there is a definite difference in size between the LR and the WMR cartridges other than just their length.

Bullet diameter doesn’t really concern us much, as the lead is soft enough to be extruded to the proper diameter for the bore by the expanding gasses without damaging any parts. The concerning part about these numbers is the difference in neck and rim diameter between the two cartridges.

Let’s imagine you try to fire a .22LR round out of a .22 WMR chamber. The cartridge will physically fit inside the chamber and the primer will more or less line up with the firing pin, so all seems well. But instead of the round fitting snugly into the chamber as it would if you had a WMR round in there the LR will be loose and rattle around more. That’s because there is more space between the brass case and the steel chamber than the designers anticipated.

The neck diameter on these .22 caliber cartridges indicates the diameter of the case from the neck to the rim because these are both “straight walled” cartridges where the sides of the case are parallel (much like a .45ACP and much UNlike a .50 BMG). That means that in a WMR chamber there’s .016 inches of extra space with a .22LR loaded versus the proper .22WMR round.

The effect of having too much space between the chamber and the brass case is pretty well understood. Too much space means the brass case can’t seal the chamber, and the result from pulling the trigger can often be more explosive (and firearm destroying) than intended. This is the best illustration of that point I could find, a perfectly good shotgun ruined because someone loaded a 20 gauge round instead of a 12 gauge round.

Here’s a slow motion look at a shotgun shell going off in an improperly sized barrel (or in this case no barrel at all).

Going back to our example improperly loaded firearm, once you pull the trigger the brass case of the .22LR round will expand to try and fill the much larger than anticipated chamber, most likely resulting in the case rupturing and splitting. Instead of all that energy being contained and directed forward, once the case ruptures the energy is free to impact the side of the chamber. More energy than normal is then directed outwards towards the wall of the chamber, and consequently the projectiles don’t go quite as far as they should. Because the case has split that means all of the force of the expanding gasses are applied directly to the chamber (instead of being retained by the brass case), and since the gases have had a moment to pick up speed before they impact the chamber wall that means that they’re moving faster and with more force than normal. The effect, as illustrated above, can rupture the chamber of a firearm.

In a low pressure round like the .22LR, this probably won’t cause the same catastrophic failure that we see in the shotgun, but it will definitely be bad for your gun and might possibly lead to some of the gasses escaping through the case head and fouling up the mechanism of your revolver. If your revolver’s chamber has been weakened (either by improper materials during manufacture or years of abuse) a kaBoom may indeed be in your future after all.

IN SHORT, you shouldn’t fire .22LR through a .22WMR chamber because the cases will rupture and you could ruin your gun, possibly exploding and killing everyone on the entire planet*. Ruger gives you a different cylinder for just this reason and I highly recommend you use it.


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*I said “possibly,” not “probably.”