Blow back technology uses a hammer or bolt that strikes against a valve. The valve releases two jets of gas. One jet blows down the barrel, propelling the paintball, while the other pushes the bolt back, re-cocking the gun for the next shot.
paintball gun's leakage of Co2 gases between the bolt and the inner barrel wall and/or leakage of Co2 gases from the cocking mechanism between the gun's hammer and inner wall of the gun's housing. Blowback may occur for two reasons. First, and easiest to fix, is that the O-rings on the gun's bolt and/or hammer need to be replaced. The second reason for blowback is more complex. It has to do with the positioning of the gun's components at the time that the Co2 gas is released into the gun's barrel.