How do you make a GBB accurate?

well. this is a tough question. for both rifles and pistols Teflon tape the outside of the barrel so it doesn't wiggle around in the outer barrel. Do the dame where the hopup meets the inner barrel to improve the seal. If you have the money you may want to consider tapping the magazines to HPA. Also, spend proper time cleaning and lubing your gun. If you have the money, spend it on some steel parts as well. I hope this helps!