Well, It is often hard to get an accurate zombie count in CA due to many of the citizenry, apearing to be zombies, but in fact just being weirdos. The latest problem though is determining if an illegal alien that becomes a zombie in CA becomes an undead citizen, or would they still be deported if captured. As for your mounting issues, I think you would have a hard time finding super large primers after the Zombocalypse to reload your 20mm, so I would just skip on the brass catcher. You know, keep it simple.