That was covered pretty well in a couple other threads but for the benefit of those new to this project, I built this rifle as an experiment to see if a mid weight 6mm bullet (75-85grains), driven at moderate velocities, would make a decent fur calling round. I anticipate minor exit wounds with bullets like the Speer 80 grain spitzer and Sierra 85 grain Game King. I am not opposed to sewing a 1.5" hole. Sewing basketball size holes gets a little old. I also wanted enough bullet to hold up to a wolf if and when encountered. Lastly, I've had an interest in the cartridge for many years.
As far as why not the 223 case. The link below explains that pretty well. The short version is the magazine on a mini Mauser is too short to really do a 6x45 effectively but it fits the 6mmx222 case perfectly.
mini mauser choices 
