Poor gas seal is why most period doubles had their chambers held short. It decreased the gap in front of the chamber and bore, so less gas leaked by, better powder burns and gave more consistent loads. Thicker paper hulls helped as well. Now the skirt on a plastic wads flares out to give you a good gas seal, so chamber length is less critical. The exception to this is reported issues with 2” shells in 2 3/4” chambers.
Fiber does not seal well enough for real high velocities. Period factory shell did not give super high velocities. To some this is a problem but I don’t see it as a major issue. Moderate ranges, that most game is shot at can be done with anything from 1100 fps to 1200fps. I shot many a duck with 1150fps lead shot loads and never had a problem. Now every factory load seems to be 1350-1500+ fps. Insane speed trying for a little extra performance.
