Most shooters are introduced to the shooting sports through rimfire cartridges. Rimfire ammunition is inexpensive, has little to no recoil and a soft muzzle report- these attributes make it great for new shooters. While 22 Long Rifle (22lr, above, left) may be the undisputed king of the rimfire market, its bigger brother, the 22 Magnum (above, right) is also quite popular.
The 22 Winchester Magnum Rimfire, also known as the 22 Magnum, 22 Mag, 22 WMR or 22 MRF, is a rimfire cartridge that has been in use since 1959. While it is still a fairly diminutive cartridge, the 22 Magnum offers a considerable increase in downrange performance over the 22 long rifle- and while this performance manifests itself in the form of more expensive ammunition, 22 Magnum is still considerably less expensive than its center fire counterparts.
I never was much of a rimfire guy. For some reason, I’ve always preferred center fire cartridges. Although, whenever I do get behind a rimfire gun I’m always left with a smile on my face.
Recently I was digging around the internet and found out Nodak Spud makes a stock to convert a Marlin rifle into a clone of the US Air Force M4 survival rifle- you can find a link to the stock and kit here. (The original, built by Harrington and Richardson, was chambered in 22 Hornet and had a 14″ long barrel, so this isn’t a correct clone, but close in function and appearance). I couldn’t wait to build my own survival rifle so I ordered a Marlin 25MN to build the rifle. It came with a 22” barrel that needed to be cut down to 16” for the build. Rather than let an opportunity go to waste, I decided to gather some data on how barrel length affects velocity on the 22 Magnum.
While I’ve done experiments like this before on center fire cartridges ranging from 223 Remington all the way up to 338 Lapua Magnum, I’ve never worked with a rimfire cartridge.
To get ready for the experiment I needed some ammunition. There is a wide variety of 22 Magnum ammunition on the market so I selected two representative loads from CCI in 30 and 40 grain bullet weights from Brownells. I marked the barrel on my Marlin 25MN at 22”, 20”, 18” and 16.5” and headed to the range.
At the range I fired 5 rounds of each load at each barrel length. After I fired each set of rounds, I used an abrasive cut off tool to cut the barrel back and repeated the experiment.
Barrel velocity data was recorded with a MagnetoSpeed V3 barrel mounted ballistic chronograph. This is an application where the MagnetoSpeed can shine. Traditional chronographs that use sky screens can have a great deal of difficulty detecting rimfire cartridges. This isn’t the case with the MagnetoSpeed. Out of the data set I recorded, I only had one round fail to register on the device and I suspect that was due to the way I had the MagnetoSpeed attached to my rifle.
Results are shown in the table below.
Findings:
Velocities were all over the place. You should also note the high standard deviations I recorded. Since I am not much of a rimfire guy, I reached out to Jim over at Ballistics by the Inch (BBTI). BBTI conducts a wide range of barrel length and velocity tests. Typically their focus is on pistol type cartridges and barrel lengths of 18” or less. They have done some work with the 22 magnum which you can find here. Jim told me, “there were some really squirrely results in there, with bigger variations than we saw in most of the center fire stuff we tested”. To look at his results, you can find the main page on 22 Magnum here and his data set with each individual shot recorded here. When I did the math, his standard deviations weren’t quite as bad as mine; however, they did have some fairly high numbers, including one at 57 feet/second. I suspect this is a function of how rimfire ammunition is made (fast and cheap) and its intended use (relatively short range).
Longer barrels don’t seem to offer much of a velocity benefit. While you may benefit from a longer sight picture and the rifle may have a better balance, I wouldn’t consider the longer barrel length an absolute necessity for the 22 Magnum. In the case of both the 30 and 40 gr loads, the 16.5″ muzzle velocity was slightly higher than the velocity recorded at 22″. For most applications, I’d guess a 16″ barrel would be sufficient.
You’ll also notice this in Jim’s data on BBTI, where some of the loads don’t show an appreciable change in velocity between 15 and 18”.
Survival rifles are cool. Check out this stock and tell me you don’t want one.
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