Current production handgun largest caliber? Ruger Super Redhawk in .454 Casull, in 9.5", 7.5", or the 2.5" Alaskan versions.
Historically? They made SRH's in 480 Ruger, which is a .475 caliber projectile, rather than a a .452 caliber projectile in the 454 Casull.
that being said, the 454 has more energy and knockdown power, due to the much higher velocities of the projectiles. 480 Ruger is between 44 Mag and 454 Casull in terms of recoil.
At least in my experience.
Edit to add: The 454 Casull can also shoot 45 Colt ammunition for plinking purposes, and is much easier to come by ammunition on the store shelves for the 454 and 45 Colt than it is for 480 Ruger.