put it this way go buy a kwa m4a1 cqb if you need more fps change the inner barrel and bucking and stop do not touch the gearbox accept if you are going to relube it.do not use a lipo, 9.6 will do just fine. Fire only on full auto in 1 second bursts, to save the cut off lever and trigger components, buy the time this gun fails you you will already be bored of it. Used guns are like college women alot of them have stds and unfortunately for you they don't make condoms for airsoft. Main message don't buy overpriced used guns unless you are an experienced player and have a drop in gearbox in case you get someone's pos. G and P makes great guns, they are like subarus, their owners abuse them and then sell them for alot, "cuz its a g and p". Do what ever you want, but that is what i would do. Btw i own a KWA m4 and will not sell it because it is that reliable.