Typically, both barrels are loaded and primed. The fowler barrel and rifled barrel combinations have been around for centuries. Thinking was if you could have "one" rifle, the fowler was the choice back in the day.
I chose the .45 cal rifled barrels for my swivel breech rifles because they are powerful rifles for the game east of the Mississippi. You can always load a .45 cal rifled barrel with a shot load for squirrel and rabbit.
Shooting the large bores demand lots of powder, more frequent cleaning, more expensive lead balls and a sharp kick in the shoulder. Range is minimally increased as force equals mass times acceleration. We can't cheat physics.
If you're hunting a Kodiac grizzly, yes, you need a large caliber rifle and some sort of shoulder padding for a pleasant day of shooting.
I love opinions and exceptional thought, economy, accuracy, quality and customer satisfaction are my primary concerns. I love what I'm doing and just try to pay the light bill.
Just my opinion guys,
Tony