A good slide or pump action pistol?

I have Loosewire; SOE Operative's slide action pistol already and i want to replace it with another pump or slide action repeating pistol. It goes only 20 ft and if i shoot it point blank I don't even feel it.  What i would like is a slide or pump action pistol that goes at least 35 ft and sort of hurts or just tell me how to to mod it to get more power out of it and a bigger mag that doesn't jam every 4 shots ( I first added more bands to the gun and it started bending the firing pin  and snapping the black hands off the red connectors. Please tell me how to fix this )    :)