It (almost) stands to reason that the moment the wad seal is broken by leaving the Gaugemate chamber and entering the larger bore, the pressure should fall off. Velocity would be affected as well with slower burning powder presumably having the most loss since peak velocity would normally be achieved futher down the bore. The kickers, in my mind, are the phenomena we see sometimes with reduced loads producing pressure spikes or detonations. What might happen with a static pressure produced by hydraulic oil or inert gas perhaps, could give dramatically different results with different powders and loads. It seems the companies that produce the reduced gauge chamber inserts have the vested interest in proving their devices may make a marginal gun safer to shoot by reducing pressures while maintaining decent velocities, or perhaps supressing data that may show negatives. It's hard to believe they put these things out there without having tested these areas of potential liability.
