'Zippo-zapper'
A zippo lighter that fires a single .22lr
Belt buckle guns, pull out a split pin and two barrel flip-out and fire simultaneously
Bolt guns, looks like a standard construction blot, but the head is spung and internally contains a .22 round which fires when the blot is released.
'Pipe gun', fires when you bite down on the mouth piece.
Buy, "Zips, pipes and pens" it's a very good book that will answer all your questions
DW