No, No, No

The length of the barrel has nothing to do with how much powder you can put in a ML. That has to do with the breech, breach plug design, and metal used. Most breech plugs are finely threaded to handle extra powder. Only thing the longer barrel does is get you more velocity over a shorter one. Probably around 25 to 50fps more per inch. And there is a limit past 28", where your increase is less and less.