A recent article in a popular gun magazine repeated a common—but dangerous—misunderstanding, and reminded me that you can’t always believe what you read.
The article was a review of the North American Arms (NAA) True Black Widow—a single-action, “mini-revolver” chambered for the .22 Winchester Magnum Rimfire (WMR), or “.22 Magnum,” as it’s more commonly known.
In the review, the author proposed that shooters who were concerned about the cost of .22 Magnum ammunition could shoot the more economical .22 Long Rifle (LR) in the gun1. Unfortunately, this is not only incorrect, it’s also very dangerous! So, in the interest of safety, your RevolverGuy team would like to remind you that the only ammunition which should be loaded and fired in a .22 Magnum chamber is the .22 Magnum2. It is NOT safe to shoot .22 LR in a .22 Magnum chamber!
Unlike the relationship between the .38 Special and the original Magnum handgun round—the .357 Magnum—the .22 Winchester Magnum Rimfire (WMR) is not simply a stretched version of the earlier .22 LR cartridge. It’s safe to shoot the .38 Special in a .357 Magnum chamber because the two cartridges share nearly identical dimensions, outside of a small variation in rim thickness and a larger difference in overall case length (designed to prevent the .357 from fitting in .38 Special chambers).
This is not the case with the .22 LR and WMR. The WMR case is larger in every dimension, compared to the tiny LR case. It’s longer, has a thicker rim, is wider, and has a larger case head. The WMR cartridge was designed to fully enclose a full diameter bullet, rather than merely grip the reduced diameter heel of the bullet, as in the LR.
Therefore, if you place a .22 LR in a .22 WMR chamber, it will be a sloppy fit. If the LR cartridge is actually fired in the WMR chamber, the case may rupture and vent high pressure gases and particulates rearward, through the breechface. There is a significant risk of injury if you fire .22 LR ammunition in a .22 WMR chamber!
What about my Convertible?
About now, some of you are wondering about the popular “convertibles,” like the excellent Ruger Single Six, which come equipped with a replacement cylinder that allows you to shoot .22 Magnum in a gun that is nominally designed as a .22 Long Rifle.
Shooting .22 Long Rifle in a gun like the Ruger Single Six is entirely safe, provided you are using the supplied .22 Long Rifle cylinder. The .22 LR cylinder has chambers that are cut for the dimensions of the .22 LR case, so there is no safety concern here.
However, it is obviously NOT safe to shoot .22 LR in the .22 Magnum cylinder supplied with the gun, for the reasons explained above. Shoot all the Magnums you want in the Magnum cylinder, but leave the Long Rifles for the .22 LR cylinder, please!
Incidentally, the SAAMI spec for .22 WMR bore and groove diameter (0.219” and 0.224”, respectively) is larger than that for the .22 LR bore and groove diameter (0.217” and 0.222”, respectively). Therefore, manufacturers like Ruger have to drill and rifle the barrel for the slightly larger WMR spec. This should really have little practical effect on LR bullet accuracy, but it makes for fun conversation around the campfire.
So, there are two important takeaways here. First, never fire a .22 LR cartridge in a .22 WMR chamber! Doing so places you and others at risk of injury, and will also lead to ruptured cases in your gun that will be more difficult to clear.
Second, be cautious about where you get your firearms information, and try to verify with another source. All of us writers make mistakes sometimes, and what we meant to say isn’t always how it comes out on paper. We hold ourselves to high standards here at RevolverGuy, and always endeavor to provide accurate information—even if it’s unfavorable to a product or manufacturer—but we’re human too, and can make mistakes. Don’t treat our word—or anybody else’s in this business—as gospel. Do your own homework, especially if something doesn’t sound right.
Shoot straight and be safe out there!
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1. From the article: “If you want cheaper practice, you can stuff .22 Long Rifles into the cylinder, a bit like using .38 Specials in a .357 Magnum;”
2. Technically, the (near obsolete) .22 Winchester Rim Fire (WRF) can be safely fired in some .22 WMR chambers, because the two cartridges share many identical case dimensions. However, industry icon—and all-around ammunition authority—Michael Bussard advises the WRF should not be fired in revolvers chambered for the WMR;
3. Cartridge specifications from the Ammo Encyclopedia, 3rd Edition, by Michael Bussard. 2011. Blue Book Publications, Minneapolis, MN. RevolverGuys are highly encouraged to purchase this excellent and highly educational resource!