Reply To: Vulcan .25
The transfer port is below that screw and if I remember correctly someone mentioned that the air can get around the barrel and the o-rings sealing the pellet probe. So when you fire and as the pellet moves forward it can affect the pressure behind the pellet until it leaves the barrel. On the .22 Vulcan that screw actually holds/aligns the barrel, but on the .25 it does not.
If it’s not the screw where the puff of air comes from then it could be the o-ring(s) around the pellet probe inside the barrel. I do not know how that is setup inside, Ernest’s video may explain.