[Hectic]

Have you adjusted the hop up?
Are you using 20's?
Most stock hop up rubbers kind of suck its something alot of folks will replace right out of the box. The hop up unit itself should be fine its just the rubber youll wanna replace. Its easy to replace. Easier in some guns then others m4's are prolly the easiest mp5's are a lil more dificult as you have todisassemble more of the gun to get at the hop up.
Lonex makes good rubbers. So does prometheus with the bridge nub.
They arent expensive.
Try to adjust the hop up and use heavier bbs (25 or 28)
Youll get much better range then with 20's thats prolly the main reason the others have much better range is heavier bbs.