I get that there is more powder behind a 357, but with a shorter barrel, that powder doesn't have the opportunity to deliver the punch it could with a longer barrel (rifle cartridges shot via pistols being the prime example). As I understand it some rounds are manufactured with faster burning powder to work better with shorter barrels. All the same, they can really only make powder so "hot" and still safe, so at some point, as the barrel gets shorter, the larger cartridge must provide only diminishing and marginal returns with some of that powder not burning before the bullet exits the barrel and not contributing to the bullet's velocity...right? I was never trying to indicate a 9 mm has anywhere near the powder capacity of a 357, it doesn't, but as the barrel gets shorter, it stands to reason that the extra powder in a 357 delivers less punch...OR maybe the powder wizards have it worked out so that it does, I am still learning.
All good points uradaisyifudo.
The cartridges themselves should never be up for debate, but what they are fired out of is definitely negotiable.
A two inch revolver is going to lose roughly 150 fps over a 4" revolver. To compensate and reduce muzzle flash I use a faster burning powder in my snub, but this will not increase velocity because the faster burning powder reaches the pressure ceiling with less powder (the pressure is more concentrated). There is no velocity increase but it does reduce muzzle flash, noise, and save money in wasted powder.
The advantage of a longer barrel with a slower burning powder is the pressure is less concentrated and distributed down the barrel. This allows for more powder which in turn increases velocity.
When I first started reloading this old guy took me out on this concrete slab with 5 different types of powder. He pored them out evenly in 5 rows about 10 feet long and lit them up. Just like you see in the cartoons
. The faster shotgun powder reached the finish line far before the rifle powder.