WELL VSR series tolerances are all over the place. The cylinders are often too small for VSR pistons so you have to do some filing. Because of this the piston may have excessive friction and tehrefore heavy performance drop. The recievers can be too thick so you need to file them a bit to fit new trigger mechs. Trigger mech parts can be out of spec or poorly cast leading to more filing. Hop up unit casting and tolerance quality is atrocious,lots of heavy burrs so It's a very poor performi...