This one doesn't go in the Z too often, but she's not a safe queen either. Since you can't buy these outright (outside of military or law enforcement) I had to buy most of the parts and build it myself (following the letter of the law, including all my SBR paperwork). Usually, HK UMPs are .45, but I converted it down to 9mm so that I could use my suppressor on it as well.
Good times. Trust me.