Help to identify 1918 DWM .22LR Factory??

[shootershack]

So I've had this for a few years sitting in the corner thinking I would get a "round tuit" one of these days so I dragged it out for some pictures and to get some help. I remember doing some Google work and finding some reference to something similar back then but for the life of me I can't find anything now (incompetent Googleing on my part no doubt). Anyway here is what I have and would appreciate any help or information that anyone could provide.

Hopefully the pictures will do the job of a description but it appears to be an all matching 1918 DWM Luger except for the grips. The barrel is 6". All numbers that I can see match including the barrel which I know is hard to see the number in the picture. The barrel has been sleeved to .22. I'm wondering if maybe the color difference at the muzzle is due to the sleeve being soldered in place? The frame appears to have been cut so that when the toggle reciprocates to the rear the frame actually splits in that area. I've pictured it open and shut. The magazine has a matching number and has a .22LR insert. It seems like my old research made reference to some kind of rare factory 22 conversion but I really don't remember for sure.

If you have any information it would be a big help. I'll want to put it up for sale eventually so history, value, etc would be appreciated.

Thanks,
Alan