One of the more interesting questions I’ve received lately had to do with handloading shotshells. The reader was aware that recipes using slower-burning powders, such as LongShot, can produce faster velocities without exceeding pressure limits than a fast-burning powder, such as Red Dot. He wanted to know why a rifle powder couldn’t be used to provide even faster velocities from shotguns.
The reason you don’t see rifle propellants slower than LongShot, Lil’Gun, H110, and W296 recommended for shotshell loading is primarily because rifle propellants are designed for very different pressure regimes than are shotshell propellants. They must work differently to succeed in their respective pressure environments. It’s not a simple “one-reason” issue, but the really big hitters in this difference can be explored with this analogy.