There’s A Lot Going On… Inside the .22 Conversion


The .22 conversion is almost as old as the autopistol itself. Shortly after the adoption of the 1911, Springfield Armory began experimenting with ways to train soldiers more cheaply and without the blast and recoil of a full-power pistol cartridge.

Early attempts ranged from a simple barrel with an offset bore that would align the rimfire cartridge properly with the firing pin, as well as an armory-made adapter with an internal bolt, before finally arriving at the Colt Ace, a blowback conversion with a full profile, hollowed-out slide that mimicked every aspect of shooting the big bore except for the recoil. Added recoil would come with the later Service Model Ace and its floating chamber, a recoil-amplifying feature dreamed up by moonshiner David “Carbine” Williams while he lay shackled at night in a prison camp in the North Carolina woods doing hard time for murder.

In truth, the advantage of the recoil-enhancing floating chamber wasn’t so much that it made the gun feel more realistic; it’s that it helped it function because the anemic recoil of the .22 LR has a hard time moving the substantial mass of a slide designed to take .45 ACP. This is not a new observation: When John Moses Browning himself saw an early 1911 conversion, he was surprised it worked, which must have been a little unnerving for its inventor.

Jeremy built this titanium Commander at Novak’s with its matching
Marvel Unit 2 conversion, which has both flush and extended threaded barrels.

The added back pressure of a suppressor can even out a sluggish conversion.
To Jeremy’s knowledge, the Jarvis shown was the first commercially available
suppressor-ready conversion. Based on an earlier Centaur Systems conversion,
it inspired the Tactical Solutions 1911 unit.

Recoil Physics

To cycle, all semiauto pistols have to strike a functional balance between the recoil energy of the cartridge and the force that holds the action shut. With blowback pistols, the combination of the recoil spring and the weight (read: inertia) of the slide keeps the action closed during firing until chamber pressure has dropped enough for it to cycle safely. Most centerfire pistols have a locking mechanism that combines the barrel’s weight with that of the slide for the first part of its travel, creating additional inertia for recoil to overcome and slowing down the opening of the action.

While spring weight matters — if it’s too strong, the slide won’t cycle, and if it’s too weak, it won’t reliably force a cartridge forward out of the magazine — the biggest problem is the slide’s weight. For comparison, a Government Model .45 slide weighs about 14 oz. on my postal scale. A GLOCK 19 slide weighs about an ounce less, while the bolt for a Ruger MkIV .22, the standard .22 pistol, comes in at a trim 5 oz. Much of the appeal of the conversion, as opposed to just buying a .22 pistol, is the familiar handling and looks, which is especially true for those of us exposed early on to the alluring idea of custom pistols matched with equally modified conversions. To keep the lines of the factory pistol, though, means a bulky, heavy slide unlikely to function. While the “jump chamber” idea works — well enough that the Army adopted a version of it for training machine gunners on .30 cal. belt feds — it has to be kept clean, and it’s not been picked up since Colt stopped production.

CZ’s Kadet conversion (now the Kadet II) takes the already low-profile slide
of the CZ75 and uses the split slide principle to make it even smaller and lighter.

The split slide design popularized by pistolsmith Bob Marvel and used in a
number of derivatives. The barrel locks to the frame via a threaded guide rod,
and the sight rib is screwed to the barrel, preventing movement.

No longer available, German barrel maker Lothar Walther produced .22 conversions
for revolvers using cartridge inserts and a barrel liner. A steel plug with an offset firing
pin machined into its face was pushed into the cartridge insert behind the .22 round.

Slide Work

This leaves lightening the slide, either by making it out of aluminum rather than steel or by significantly reducing its profile. For decades, the big kid on the conversion block was Jonathan Arthur Ciener, who took a raw block of aluminum to a mill and carved it into a .22 slide. It worked well enough he made 1911, Browning Hi-Power, GLOCK and Beretta conversions and subgun and rifle units.

None of the pistols locked back on the last round because a steel slidestop being rammed up into an aluminum notch while the slide is still cycling is fated to chew it into nothingness in short order. Thus, you counted your rounds and did your best not to dry fire it so you won’t score the chamber. A later advent adopted by others who use aluminum is inserting a hardened steel insert in the slide capable of stopping the slide and living.

The challenge in the .22 conversion is finding a way for the anemic recoil of
a .22 LR to cycle a slide sized for a big gun. A 1911 slide weighs nearly three
times as much as the 5 oz. of a Ruger MkIV bolt.

Using aluminum for the slide reduces weight, but it takes a beating. This one
consumed a brick a week for quite some time. Unsightly but not a functional issue.

The .22 conversions have long been an option for European service pistols,
such as this Walther P38 conversion. The subcaliber barrel insert is a typical
feature on many continental conversions.

Split Slides

While you lose a bit of the aesthetics, and more of the handling, a split slide similar to S&W’s Model 41 target pistol makes for a lower-profile slide light enough to cycle even when made of steel. Conversions for pistols other than the 1911 have adopted the split slide, such as the older Peters Stahl units for S&W’s Model 39 and the CZ75 Kadet conversion, which is perhaps the single most reliable unit I’ve ever spent time with.

Pioneered on the 1911 by Kart and Day, followed by Marvel, the split slide also means better accuracy. Generally, a pistol’s barrel, frame and slide, to which the sights are attached, all move separately. The inevitable tolerances among those parts change where the bullet hits as the barrel moves relative to the frame, as well as changing where you aim as the sights move independently of the barrel.

Mounting a sight rib directly to the barrel, with a separate slide cycling beneath it, eliminates that variance. The Marvel unit goes one further, using the recoil spring guide rod to lock the barrel down firmly to the frame. I’ve used Marvel conversions for over 20 years, through at least four significant variations, and they remain spectacularly accurate, capable of 1/2″ at 50 yards with the right ammo. Used successfully at the Camp Perry National Matches, Marvel offers an aluminum full-slide conversion better suited for CCW training and the split slide Unit 1, which comes in steel or aluminum. They also make dedicated .22 LR receivers in either material.

In my experience, the Marvel Unit 1 is unmatched as a marksmanship training tool. When your gun can shoot MOA, missing that clay pigeon on the 100-yard berm is your fault, not the gun’s, and the relatively cheap cost of .22 ammo means you can keep trying all day long.

Colt’s answer was the floating chamber, a recoil-enhancing device
dreamed up by David “Carbine” Williams.

For the ultimate in rimfire fun, Kirst Konverters offers rimfire conversions for
popular blackpowder revolvers, which is next-level cool.

Strikers And Hammers

In addition to slide weight, striker-fired conversions such as the GLOCK further play havoc with a conversion’s delicate balance since the recoil spring has to push against the force of the striker spring for the slide to go into battery. That’s not an issue with the strong recoil spring of a 9mm or some such, but it matters when the spring has to be rimfire-light.

It was no surprise when S&W introduced the M&P .22 with an internal hammer rather than a striker. Using a lighter hammer spring reduces the resistance the slide has to overcome to cycle on a hammer-fired pistol since the fallen hammer holds the slide forward. Similarly, adjusting the radius of the firing pin stop is an old-school way to adjust a pistol’s cycling since that curvature affects the force required to cam the hammer back into the cocked position.

Tactical Solutions .22 conversion shown on a Gen 3 GLOCK 19.

Jeremy shot this 1" group from 25 yards, resting his hands on the bench and
using a Holosun dot. He’s shot smaller groups at twice the distance from a
Marvel Unit 1 held in a Ransom Rest.

Pachmayr sold private labeled Peters Stahl conversions for the 1911, Hi-Power
and S&W Model 39, the three fighting guns of the day.

Magazine Challenges

As with all autos, magazines supply their own cohort of problems. Most .22 pistol mags traditionally hold 10 or fewer rounds. This has little to do with magazine capacity rules but with the rim on .22 LR cartridges. As rounds stack against one another in the magazine, they push the lower cartridges down at a more extreme angle, which makes for challenging feeding. If you’ve ever wondered why classic .22 autos like the Ruger Mk series, Colt Woodsman, High Standard, etc., have raked-back grip angles, it’s because the angle makes for easier feeding than the more-or-less 18-degree grip angle of most defensive pistols.

Magazine spring tension also plays into it: A too-weak spring will not pop the cartridge up in time for the slide to pick it up on its way forward. Or, sometimes, not hold the cartridge against the feed lips when the slide hits the end of its rearward travel, letting the cartridge spurt forward loose into the mechanism. At its most extreme, the gun will eject the empty casing and the top live round in the mag out through the ejection port before feeding the next round in the mag, which is annoying but hilarious to watch.

The answer is not as easy as just putting in a strong spring because the top cartridge rubs against the disconnect rail on the bottom of the slide, creating friction that slows it down. It probably goes without saying conversions tend to prefer hotter ammo.

There is one easy solution to many of these challenges: a suppressor. The added backpressure of a can gives enough extra oomph on firing to even out conversions that otherwise cycle sluggishly. However, they can also blow unburned powder and debris back into the shooter’s face through some of the split slide designs. As I said, a lot is going on in there.

For more info:

Subscribe To American Handgunner

Purchase A PDF Download Of The American Handgunner March/April 2023 Issue Now!