My answer was a little too short. A drop in might have some benefits over OEM, but a fit barrel will give you the best accuracy improvement. I've tried all the Glock barrels and KKM gave me the best accuracy. I fit a semi-fit Barsto barrel to my GGI 3.9" gun, but the chamber was too tight. Barsto fixed it, but now its pretty sloppy. I haven't had time to shoot any groups with it, but it feeds everything.