I've found a more extensive biography on Ulrich von Schellenberg, here:
Unfortunately it is in German script so I can't transfer it to Google translate for the usual quick-and-dirty translation. I wonder if there are any free German script OCR programs out there so I could at least turn it into characters to enter an automatic translator? I can transliterate German script into more useful font, but takes more time than I have.
I'm not going to bother Michael about this one, he's already spent enough time translating this stuff.
I've also thought more about the "JUR" marking on the gun. I still believe it will be impossible to determine, with certainty, what that stands for, however it is almost certainly from a later period than the "1525" estimated date of manufacture, as Michael has said. One reason we know that is because the letters were crowded into a nice open space intentionally left above the coat-of-arms so the c.o.a. would be reasonably centered in an open (plain undecorated) area. I think the letters indicate a subsequent owner, after Ulrich had left the battle zone of northern Italy ca. 1529. It is possible that it was captured at some point, or more likely simply retained by whatever Swiss mercenary was using it, probably with Ulrich's consent. Or perhaps it remained under control of Ulrich's commander, General Ramon de Cardona. Who knows.