This movie shows the underside of a Walther LG 400 breechblock. When the hammer is released (at 49 seconds into the movie, sorry for that) you can see it bouncing 2 or 3 times. Each bounce may open the valve more or less and release some air which is not effectively used to propel the pellet because this has already started off in the barrel. Reducing hammer bounce can save a lot of air and increase the number of shots from an aircylinder fill. I made an anti bounce hammer for my Airarms S400 FAC which increased the shotcount from 38 to 68 shots per 200 bar fill.