Not sure I get the point of the same caliber. Handguns and rifles have very different design constraints, because they have different intended uses (in general).
Handguns are designed pretty much for portability, concealability, and the ability to operated with one hand. Long guns don't have those constraints.
Long guns don't need to be (as) portable, (as) concealable, and are designed to be operated with two hands and a shoulder.
When I look at handgun rounds, they tend to be short and relatively wimpy - when viewed from the point of a rifle caliber.
When I look at rifle rounds, they tend to be long and hard to control - when viewed from the point of a rifle caliber.
To each his own, I guess. When I look at handgun rounds in rifles, or rifle rounds in handguns, they look to me like those boat/car/plane combos that were a big deal in the late 50s.
Mike