[ILLusion]

taping the port should technically offer very little or no positive benefits whatsoever. There is still the gap between the inner wall and the outer wall where air can pass through as the o-ring passes the port.

Although compression would begin at the very start of the stroke, as soon as the o-ring reaches the start of the port, the seal would be compromised until the o-ring reaches the end of the port.

There may be other effects happening, such as the piston starting the launch of the projectile - followed by a break in projectile acceleration as the piston head reaches the port, causing the piston to accelerate to an even faster speed so that as the seal is closed at the end of the port, it will finish off the compression cycle to launch the projectile at a higher speed.

I would not recommend this as a permanent modification. The o-ring passing by the tape repeatedly may eventually smear adhesive on to the o-ring and across the inner wall of the cylinder.