Many years ago at Friendship, a fellow had made a side slapper .It was real simple it had a long ( 12") spring steel rod hooked to the side flat of the barrel . Where the drum or liner would be , was the nipple in the side flat of the barrel . It was a single trigger with a rod going thru the stock behind the breech . The rod went just in front of the trigger and had a notch it and when you pulled the trigger it pulled down and the spring steel rod slapped the nipple. Well you get the idea . I have one under construction, and found that a trunk rod from a small car works great for the long spring steel slapper . I found several cars have the trunk rods. They are used as a spring to ease the trunks up and down . These could be used for several things , they are around 1/4 to 3/8 Dia. and the stright section is about 3 foot long .