I really wanted a .22lr 1911 trainer, and given all the options, I went with the offering from Rock Island Armory (AKA Armscor)
They mounted an interestingly designed upper on one of their standard .45acp frames, and market it as the XT22.
http://www.galleryofguns.com/genie/default.aspx?item=51930
http://www.budsgunshop.com/catalog/...guns/ARMSCOR+PRECISION/API M1911A1 XT22 22LR/
http://www.armscorusa.com/index.php?option=com_content&view=article&id=7&Itemid=18 (22 and 45 combo - interesting, but I just have the .22 and a couple .45 guns on Officer frames)
http://www.armscorusa.com/index.php?option=com_content&view=article&id=6&Itemid=17 ("standard" ... what I have)
So far, my XT22 has eaten 450-500 rounds of CCI minimags (no issues), 40-50 rounds of various other CCI hotter loads(no issues), and runs nicely on Fed550 bulk as well (the cheap stuff from WalMart, very few issues, some Fail to RtB and a few ejection bobbles)
The magazines are available from RIA for a reasonable price, and Kimber rimfire conversion magazines fit (but don't drop free) and feed.
RIA took a different approach and just mounted a quality conversion kit on a frame for you, rather than making the slide out of
lighter material, they made it out of
less material, and I think out of higher quality material. Zamack has some uses in firearms, but given the option for a spiffy design and steek or a cheapo design and Zamack, I'd rather have steel from a known good manufacturer in this application.