If you’re looking at a .22 conversion kit, I’ve found Marvel Precision’s “Unit 1″ 1911-22 kit to be accurate and reliable, although their customer service is somewhat lacking.

Marvel 1911-22

Marvel Precision offers a .22 conversion kit for the STI 2011, the gun I shoot in competition, as well as Para Hi-Caps and 1911 single stack. The only difference between the kits are the magazines, the 2011 and the Para are Hi-Cap 1911s. The kits start at $429.00 and go up depending on what options you choose.

201105011842.jpg
The difference between the Marvel kit and most other 1911 conversions is that the barrel is fixed in place, and a big chunk of the slide is part of a non-reciprocating sight rib. That means that, unlike most conversion kits, you don’t have to use high-velocity ammo for the slide to cycle. It also makes the gun very accurate. It comes with a 50-yard test target to prove it (mine was pretty tight!).
Marvel offers a compensator for the barrel, as well as different sight ribs including one with an integrated Picatinny rail for mounting optics. Throw a C-More “Railway” on there and you’ve got yourself a heck of a Steel Challenge or RRC racegun. The rib that comes standard has a Bo-Mar clone adjustable rear sight and a black serrated front, but I added a red fiber-optic sight to mine.
201105011859.jpg
The fixed barrel/sight rib.

The standard barrel has a hole tapped in it for Marvel’s proprietary compensator. Marvel also offers a threaded barrel to allow the use of a suppressor, (Clancy fans remember John Clark/Kelly’s weapon of choice in Without Remorse) such as Gemtech’s Outback II .

Magazines

The magazines for the single-stack kit are for the old Colt “Ace” conversion and hold 10 rounds. The 2011 mags are the same Ace mags in an adapter block so they’ll fit the wider 2011 double-stack frame. However, the 2011 mag adapter does require some fitting if you want it to drop free (how-to coming soon), and the adapter blocks aren’t available on their own.
201105021554.jpg
The magazines are pricey, $58 for a metal single-stack mag ($30 for a plastic mag) and $63 for a double-stack STI or Para magazine, although they are cheaper than other conversion kit mags such as the ($105) Tactical Solutions 2011 conversion mag.
Gun Compatibility

The conversion kit will fit any 5” 1911, 2011, or Para. Marvel also offers a “Commander”-size kit for 4” 1911s. If you have a 1911, a 2011, and a Para you can use the same kit, with different magazines. BUT if you have a C-more sight on your gun, the kit won’t fit. That’s because, for some reason, there’s a big ridge behind the slide-stop cutout. That ridge will hit on the C-more mount and the kit won’t slide onto the frame.
201105021659.jpg
Note the ridge behind the slide-stop. Unnecessary!
201105021659.jpg
That C-more mount will hit on that ridge on the conversion kit. Note that this normal 1911 slide doesn’t need a ridge for the slide-stop.

I’m sure if you wanted to you could file the ridge off and make the kit fit, but a better option would be to put the kit on another gun and order the Picatinny rail sight rib.
Another issue with the Marvel kit is holsters. A “race” holster like a CR-speed or Ghost holster won’t have any issues, but a normal holster might hit on the sight rib. I know the more tightly-molded Kydex holsters (Blade-Tech and most custom holsters) will hit on the rib, and the barrel (slightly longer) will hit on the bottom of closed-bottom holsters. I have found that Blackhawk! SERPA/CQC holsters will work, as will 5.11 Tactical holsters (made by Blade-Tech!).
Customer Service

My Dad ordered this kit at the SHOT Show in January. I got a call asking me to pay for it and for a shipping address in early March. Then, they proceeded to use Dad’s business card (as president of a 12-bay pistol range, our address written on the back) that he gave them at the SHOT Show as the shipping address. Mid-April he gets a call asking again for a shipping address because they sent the kit to 12th Bay Street, Pistol Range, UT. Seriously?! If I’d known it’d take that long to get the kit, I would have gone with a Tactical Solutions!
Similar Kits

Several makers offer kits that are similar, if not identical, to the Marvel kit. I haven’t got any experience with these kits, but I’m sure they all work just as well.
Bob Marvel, the designer, started another custom gun company (not affiliated with Marvel Precision) that offers an identical kit. Nighthawk Custom, Advantage Arms, and STI International all offer one rebranded as their own. It goes for about the same as the Marvel Precision.
Tactical Solutions also offers a similar kit, but as I mentioned earlier, the magazines cost an arm and a leg. I’m pretty sure that the Marvel mags will work with it if you wanted to buy additional mags. The kit itself sells for about the same as a comparable Marvel, and all the same options are available. It runs normal .22 ammo just like the Marvel kit.
Marvel Precision also offers a “Unit 2″ kit that will fit any 1911 holster but requires high-velocity ammo to cycle.
Conclusion

Marvel Precision makes a fine .22 conversion kit, plenty of accessories for it, and the cheapest conversion kit mags around. I’ve only had a few issues with reliability and those were all user error. But, if I had to buy another kit, I’d probably go with a Tactical Solutions or an STI International kit entirely due to Marvel’s poor customer service.