Originally Posted by Wycke
I've seen/heard that reported as well, but I don't buy it. The ball is accelerated by the pressure of the propellant (air or CO2) behind it in the barrel. Once it leaves the barrel, the air pressure is dissipated to the surrounding air and the ball begins to decelerate. Depending on the volume of the propellant, there could, theoretically be a final burst of acceleration as it exits the barrel immediately after the ball, though it wouldn't have any significant effect on the overall flight of the ball.
Smart Parts used this phenomenon as basis for their claims that their All American barrels were the most accurate. The second half of the barrel, just like the "front" of their freak barrels, was bored to .700. The spiral porting was purported (no pun intended) to direct or control the escape of this pressure, reducing the turbulence that the ball might experience as it left the tip of the barrel. Further, they claimed that the spiral arrangement of the ports imparted a spin on the ball to improve the accuracy of the shot. They never provided any scientific data to back up any of these claims, but at one point in time everyone and their mother had an AA on the field. Advertising is an extremely powerful tool.
In fact, I believe a few years ago that either Doc, Have Blue, or some other airsmith used a high-speed camera to capture the plume of vapor following a ball out of the tip of an AA barrel and also show that almost no vapor exited from the porting. I don't know if they also debunked the "spin" part of SP claims, though.
I seem to recall photos of baby powder blowing out ports. The phantom porting looked impressive. Then again, I suspect there was a pretty large margin of error going on, since another barrel(can't remember which) that I thought would "do well" simply from the design... didn't.
I think porting is a sound signature benefit only. That, and it looks cool.