Retro Arms Built this Hop-Up chamber on results from testings, so this chamber is precise and custom-made constructed for best feeding and performance. We changed drill depth, so with 20,1 mm nozzle and Hop-Up 60 Shore bucking, we were able to get stable performance above 16m/s above spring power. Even feeding with heavy weight 0,43 BBs on SEMI and AUTO was without any problem.