These days, with ammunition availability being what it is, interest in .22 kits has spiked. As it turns out, Aguila makes a .22 kit for your .22. The Colibri is a .22 LR case loaded with priming compound and a 20-grain conical-point cylindrical bullet. Being significantly less powerful than, say, BulkFed .22LR - the muzzle energy difference is more than an order of magnitude - these rounds don't even play at cycling the action.
Judging from Midway's customer reviews, the Colibri (and its beefier cousin, the Super Colibri, which has received the Carteach0 treatment here) is something of a sleeper hit. It seems to fill two distinct niches: training and pest control. The former is the focus of my interest.
At less than 10 foot-pounds of muzzle energy, any backstop built strongly enough for airgun pellets will suffice. A mailer box stuffed with old clothing, shot end-to-end (about 14" of padding), with some paint cans and a heavily-insulated load-bearing wall behind it, worked just fine.
I can see a potential issue with mixing up .22LR and .22 Colibri rounds, which would of course render said backstop pretty useless. While unlikely, verifying each round's identity is probably sound.
As expected, the Colibri turned the Ruger MkI into a caliber .22 straight-pull bolt action (with automatic bolt return!) airgun. The average velocity from a 4.75" barrel was 428.5 fps, which is nearly the same as my Diana Model 25 in .177 (though with twice the projectile weight). I had much better luck than Carteach0, with an extreme spread of only 48.65 fps (for very generous values of 'only,' mind you...) and a standard deviation of 13.37. At back-of-garage ranges (20ft was all I had to work with) this doesn't appear to affect accuracy too terribly.
In a word, usable. As a short-range, minimum flinch, limited backstop training and practice round, it serves my needs, which is to say it shoots better than I can. My best group (offhand, slow-fire) measured .61" at 20 feet. That is more than sufficient to hone my skills, especially neglected ones like strong and weak hand shooting. If I ever get to Bullseye-level shooting (ha!) the round may prove insufficient.
The group was below and about a centimeter left of the point of aim. Knowing my personal tendency to skew the sights left, and that I was using a 6-o-cl, ock hold, this is probably shooter-induced.
The Ruger magazine did not play nicely with the Colibri. The rounds tended to curve in, such that the top round would be pointing several degrees down into the magazine. Passable results were obtained with no more than 5 rounds in the magazine. Fortunately, the Ruger seemed to be very forgiving, chambering rounds way out of the ideal feed position.
For optimal results, exuberant extraction is recommended, unless you want to incorporate type-III malfunction clearance drills into your practice regimen.
Compared to a .177 air rifle (10gr at ~430fps) the Colibri was slightly louder, and sounded like a quiet gunshot rather than an airgun. In an enclosed garage the air rifle is quite comfortable; the .22 round scratched the top edge of the comfort zone. If you're plinking in the garage, earplugs are a good idea.
Recoil? Oh, sure, there's recoil. And about 2mm of muzzle rise, even.
I like this round a great deal, for several reasons. It bridges the gap between dry-fire and range day, allowing you to apply what you've worked on without leaving the house. When training new shooters, you can let them practice fundamentals on a real gun, with extremely mellow noise and nearly nonexistent recoil. For very sensitive shooters, the difference between a .22 CB and a .22 LR is pretty noticeable, especially indoors. Furthermore, if you can shoot in the garage, you can avoid the usual range hubbub. Nothing distracts like someone lighting off a .357 SIG or a 7.62x25mm in the next stall.
Seasoned shooters can benefit, too. You're shooting with your actual gun, rather than a separate airgun. Thus, the same grip, sights, trigger pull, etc. apply. Michael Bane sounded off on this topic a while back. In fact,a carry gun with a .22 kit shooting .22 Colibri allows you to do everything not requiring semiautomatic fire in the comfort of your garage (allowing, of course, for backstop considerations. At some point in the future, I'm going to go all Box O' Truth on some surplus wallboard and see what 'backstop' really means in this case.) Being able to draw, press-out, and then confirm that there's a hole where it should be sounds like good reinforcement to me. And with the doors closed, no one outside the garage is likely to notice what chicanery you're up to.
It looks like I have yet another kind of ammo to stockpile, now.