Karl: what,
exactly, is the chamber length?
Using long shells in short chambers
will raise the pressure.
Bells' study was 12g and the increase ranged from about 400 psi to 1200 psi.
It is here about 1/3 way down
https://docs.google.com/document/d/1...vwLYc-kGA/edit
I am not aware of any study of modern 16g or 20g shells.
And if the mouth of the shell enters the forcing cone, recoil will be increased.
We've had this discussion on the 16 gauge site, and a fella did some dumpster diving and measured the spent shell length of several brands. He reported that the Fiocchi shells were shorter than 2 3/4".
Possibly someone could measure some empties and report?