Heres how i did it...
the pack a punch needs to be at the back of the lighthouse. also the mystery box needs to be there aswell.
What you do is... put your unupgraded raygun into the pack a punch,(you now have no raygun for about 10seconds) then quickly spin the mystery box. if your lucky, you will get a ray gun in the mystery box. once you see the ray gun in the mystery box, first get your upgraded raygun from the pack a punch and then grab the raygun from the mystery box. walllaaaaaa you have two ray guns. this happened to me. and i was very surprised XD so technically speaking, you can have 8 rayguns in one game. and two scavengers etc etc