Ive shot max 120gr loads of BH209 in a 20" barrel with very little velocity loss vs a 24" and the fps was still increased vs 110gr. You can get a full or near full burn in a 24" barrel under the correct conditions.

Im am normally using heavy bullets (300gr+) though which help get a good burn. Ive shot even higher loads in special built rifles made for extreme pressures but i normally only recommend those to very well educated ML enthusiasts with very good quality barrels.

BTW don't get caught up in the MAG load craze. I only do it because my rifle shoots that load very well. Many max loads will not shoot as well or require a lot of tinkering to get them to shoot a max load as well as say.....90-110gr loads.

Shoot what gives YOU the accuracy YOU need for YOUR hunting situation. 70gr of real BP has killed more game than you can imagine and it did it very humanely.