Just a simple semi-auto design by Oblivitus from his K'nex Concepts. I have to say, I think that this is not quite as easy to use, powerful, or useful than his other pseudo semi-auto design (stacked barrels rather than side by side ones). It's cons hugely outweigh its only pro (pseudo semi-auto). It's hard to reload and shoot and you can't add more bands without taking it apart. If it is ever updated, (and if I ever put more time into it,) these problems could be solved. However, it is very fun to use.