I would go with a 44 Magnum personally. It has distinct advantages in off-the-shelf ammo options over any other cartridge in the same class. I would suggest a barrel length for a revolver of 4 3/4 to 6" but I would personally opt for the shorter one. I would't go below that length because they get too hard to shoot accurately at any distance given a short sight radius and the thickness of the front sight relative to the target. I don't care for DA guns so I would be looking at a Ruger or BFR. At the end of the day, plan on spending a lot of time shooting the gun if you want to be proficient with it.