Been doing research today, its always good fun! I'm trying to create a catapult for firing m&ms – like you do. The picture is of the second prototype. At the moment I'm doing a catapult rather than a trebuchet design because I really don't want to use string in the design. I'll see how it goes.

Anyway, second draft uses a a stack of coins as a counter weight. There is a shaft, with a cup on one end for the m&m. The other end is attached by a paper hanger to the stack of coins. The long part of the shaft is 10x the length of the short section. It works okay but at the moment it flings the m&m only about 2.5metres (7ft). I'll be trying some variations tomorrow. Things to try: change the ratio of lengths, increase the weight, add a flailing arm, like a rigid trebuchet. Another progress report soon.