I recently picked up an Advantage Arms .22 LR conversion kit for my new Glock 21. It seems like I'd kind of reached a plateau in my shooting abilities, and I decided the only way I'm going to get substantially better is to shoot quite a bit more. Given my current finances, I'm not able to afford a lot more .45 ammo (though I am thinking about getting into reloading), so the idea of being able to shoot for about 2 cents a round, rather than 25, was pretty appealing. I've read good things about the Advantage Arms conversion kit (here and elsewhere on the net), so I decided to go for it. I had quite a bit of trouble actually finding a place that had the kit in stock. The Advantage Arms website says they aren't selling direct at the moment because they have so many backorders, and most online stores selling it are backordered as well. I finally ended up buying one on eBay.
The conversion kit consists of a replacement slide, barrel, recoil spring, and magazine (plus a cleaning kit). Changing calibers only requires removing the full caliber slide assembly (just like the first step of field stripping the pistol) and sliding the .22LR assembly on. It only takes a few seconds. I've ended up swapping back and forth between .22 and .45 half a dozen times during a range session with no trouble. The conversion slide uses a straight blowback operation, rather than the Browning short recoil action used by full caliber Glocks. The slide is quite a bit lighter than the original Glock slide, presumably to allow the relatively wimpy .22 LR cartridge to cycle it. Advantage Arms makes two versions of their conversion kit, a "LE" model where the slide has the same dimensions as the standard Glock one, and a "Target" slide which is shorter, with upswept ends where the sights are mounted. I've got the LE version.
So far, I've put over a thousand rounds through my Glock with the kit attached (two bricks of .22). I'm not really a good enough shot to say how accurate the conversion is, I can just say that it's more accurate than I am. It has definitely improved my accuracy though. I'm not going to be taking any 50 yard headshots, but doing all this shooting has basically halved my group size for sighted slow-fire in the 7-15 yard range.
While I mainly got the conversion to work on my sighted fire skills, it also seems pretty useful for working on my point shooting skills. So far about 2/3 of the rounds I've put through it have been sighted fire and the other third has been working on point shooting, particularly from retention and partial extension.
My biggest complaint about the conversion so far is the frequency of jams. Part of the reason I waited to run a second brick through the kit before posting a report is I wanted to keep a count of how frequent problems actually were (I didn't want to overstate the problem). Based on my second brick, the gun jammed about once every hundred rounds for the first 300 rounds, and about twice every hundred rounds from 300 to 525 rounds. The most common jam was an odd failure to extract where the round gets lodged in the ejection port backwards, though there were a few stovepipes in there as well. Obviously, this would be unacceptable accuracy for a self defense gun, but for training it's something I can deal with.
The only other complaint I've got is more of a minor quibble. Empty .22. mags don't drop free, and have to be pulled out by hand. It would be nice if the gun were a bit more realistic when it comes to mag changes (maybe weighting the mag somehow?)
One thing I'm thinking about changing are the sights. The kit comes with a set of Glock adjustable target sights, which have a dot for the front and a movable U-shaped white piece in the rear sight. My Glock 21 has trijicon night sights on it, so I'm used to a three dot sight picture. I think I'd like to swap the rear sight out for a three dot one, so the sights are closer to the ones on my carry gun. Does anyone make an inexpensive set of three dot sights for Glock pistols?
Overall, I'm quite pleased with the conversion. The ability to shoot a lot more seems like it's going to really help my shooting.