Is it just me, but I have been wondering why S&W doesn't come out with an upper in .22 mag or .17hmr. Seems to me that it would be a big seller. I e-mailed them about it several months ago and they said they had no plans to do so.
If you're looking for a .22 upper, I highly recommend one from Nordic Components. Mine eats anything I feed through it, as fast as I can pull the trigger. The guys who work there are also top notch. The website says they will be coming out with complete rifles soon too.
As you may note, from looking around at the other manufacturers, the semi-auto rimfire magnum platforms have yet to perform well enough to warrant the engineering resources and production capacity to do so.
The Keltec PMR30 22 mag pistol has had some serious problems that caused them to pull it for a while after introduction. Even Ruger has had serious issues, as they never really got their 17HMR version of the 10/22 to market (to the best of my knowledge).
The 22 Mag/17HMR are much higher pressure rounds and, IMHO, should be left to single shot or bolt action guns.
check out what Hornady has to say: