I thought I should probably add the latest version of the chart showing the effects of various ways to tune a regulated PCP....You will notice that the grey line (tuning on the downslope) shows the shot-to-shot variation in velocity often experienced with this type of tune.... Any small variations in hammer strike are amplified because the valve is barely opening.... With this type of tune, the gun is using tiny "sips" of air at higher than the required pressure.... It is very efficient, but prone to this phenomenon....Bob