well...
...back in the 1870s, believe it or not, someone did a two mile shot (hitting a 6' diameter circular target). 1000 yard matches with low-velocity .45-70s, .45-90s, and .45-120s were once common too. The bullet WILL go that far, you just have to angle it up far enough.
Now, I don't think the average soldier was meant to be able to hit a man at 2000 yards. When the bulk of these rifles were designed, in the late 1800s, many armies were still using very Napoleonic tactics, and one of those tactics is to have your formation of troops line up and fire a volley at the enemy formation, while they're a long ways away. I'm guessing volley fire is where this was supposed to be applied.
Also, the reason many old rifles area very long is becasue they were meant to be used as a pike against mounted cavalry, with the bayonet installed.