I did some testing on "wad-pressure" it takes a minimum of 60 pounds pressure and a sabot tight enough to hold it to maintain minute of angle accuracy.
With the vent liner installed and the channel between the 209 and the vent-liner drilled with a #21 and polished has reduced the carbon problem to cleaning it out when I clean the gun after shooting and my numbers and targets show an improvement in consistency so my opinion is that I am also getting either better ignition or more consistent ignition.
Mike did a very similar vent liner install maybe he will comment on this for us. Lee