Barrel taper maybe a real factor I can't rechamber one of my p17 Enfields to 300 h&h because the rapid taper passed the orgianal chamber.at least the was the suggestion.the only way the 120 shines is in black powder.otherwise the powder gets lost in the case.but there are a lot of 45-70/90 "express loads" out there.didnt know if anyone has tried to lean on the action.they don't seem worried about pre20th century steel or some Italian crap the probably has pin holes inside of it.