I was prepared to respond to a comment by a new member on ripoffs and remembered one of junglejim's threads...I found it but Jim has not posted in over nine years...
It involved a Luger carbine...
http://forum.lugerforum.com/showthread.php?t=21822
IMO, it should be a sticky, and a warning...
But that is not the thread I wanted to talk about here...
Jim posted pics of his .22 Luger conversion done by John G. Lawson which used a custom wildcat .22 bottleneck cartridge. I do a bit of wildcatting and found it interesting. Some of the newer members (and RickW and Sieger) may find it interesting as well.
http://forum.lugerforum.com/showthread.php?t=22199
If junglejim is still around, perhaps he could expound on this fascinating conversion...