Why did I lose my gun on Call Of Duty Kino Der Toten Pack A Punch?

LOL cus i did the exact same thing the other day not even joking! i lost my only gun so i had to run around with my pistol and knife. yes, PaP is just like the mystery box, leave your gun too long and the machine just reabsorbs it? I know it sounds wierd and its annoying but yeah lolz.