Calculating the hold over is the hardest thing. A magnum cartridge would have less drop making the hold over much easier. I shoot pistol at hundred routinely, mostly 45acp which is sighted in for 25 yds, selecting an aiming point is without a doubt the most challenging part, it's usually the top of the target frame which is obscured by the sights.
Holdover (selecting an aiming point
above the target) is the
worst way to get hits at long distance. It's a little better than closing your eyes and hoping the Force makes the hit, but not a lot.
When you cover the target with the sight, or muzzle of the gun, you lose all reference to your target. You know you are aiming above your target, but you cannot see HOW MUCH above, or how far right or left you are, because you cannot see the target.
Holdover works pretty well when shooting a rifle or pistol with a scope, where you can raise your point of aim (center of the crosshairs) above the target, and still see the target in the scope's field of view, but it is about the worst way to aim when using iron sights!
Use the barrel or slide itself as part of the front sight and there is no holdover.
Hawg knows how to do it right!!
Don't cover your target with the gun, put your target on top of the front sight, and keeping it there, raise the sight above the level of the top of the rear sight.
How much you need to raise the front sight is what you need to learn, through practice (trial and error), because it will be different for each gun, load, and distance, but, once you learn it, it is a constant.
For my Ruger Blackhawk, raising the sight (with the target on top) until the slope of the front sight "breaks" (the slope of the blade turns vertical) being level with the top of the rear sight is just the right amount for hits at 200yds.
Shooting a Browning Hi-Power, using the same method, a spot on the slide, about an inch back from the front sight, level with the rear sight, produced 200yd hits.