The Raptor case Bertrum has in stock now is longer than the Excal case but has the exact same case capacity.
Not sure but I think the first ones Kirby got made had more case capacity, then Bertrum changed something ,maybe trying to make it stronger in the case head witch reduced case...
I have both the Raptor case and the Excallibur /Jamison brass and they are both identical in case capacity .
Quality cartridge brass is about 20 grains less capacity.
What brass are you using? Whats it head stamped ?