In the 1960s there was a wildcat that looked a lot like that, the .22 Goldstein Luger. Jerry Goldstein necked down some 9mm and/or .30 Luger to .22 and put a barrel for it on a P08. I never saw but the one magazine article and did not think it had gone any farther.
I do not recall him editing headstamps but he might have.
Or this might be a factory product with an improvised headstamp bunter giving the differences you describe. (I can't see the headstamp in the picture well enough to read.)