Um, if it were me, I would judge each gun individually or as a group in a gun era. I am not too sure about 20 bore, but hopefully Hause will stop by & inform us. But I am a huge fan of Gamebore, specifically the shot if loaded with the Diamond Shot, but Gamebore is notoriously Hot. I live on the edge & I would cap pressure for most barrels @ 7500 psi. Now you might be referring to Regal? Armusa is always a Great option and then always consider RST, when, where available. The platform lockup, tube steel, etc. are all factors.
Serbus,
Raimey
rse
