The Ravager is the most powerful K'nex gun I've made. It has a range of almost feet (with the right bands) and has a pretty quick rate of fire for a non automatic gun (meaning you have to pull something back each time you want to fire).
Comfortable fore grip
Mag as handle (for more power)
Sturdy, comfortable stock
Can be modified to shoot exploding rockets!
Ugly mag pusher
Non removable handle/mag
Uses three broken pieces
I hope this gun has given you some inspiration for some of the mechanisms for your guns. I can't make instructions (I might later though) as I don't want to risk disassembling it because I have no clue how to reassemble it.