Hey, you're talking about me!!!
marksman13 is right when he says it involes
"skill, science, and luck".
However, there is a lot of mysticism that surrounds long-range shooting because so few people get the chance to do it. And thus we get a lot of replies like how you need a 50BMG to make hits at 1000 yards and only a super ninja monk can do it. On the other side, there is false bravado those that claim they can shoot 2" groups at 800 yards
all day long with their Dragunov. The truth is somewhere in the middle.
I have taken a new shooter who has never shot a long-range rifle before, and had them hitting a 1000-yard silhouette in under 10 minutes... with my gun, ammunition, and data.
As other have said, you need a cartridge that will make it to the max distance before going trans-sonic, and you need a rifle with sufficient mechanical accuracy, and then it's
all you. The other issue is the air density, which can change the max effective range of a cartridge 500 yards or more (from a cold day @ sea level to a hot day at 8000').
Super-duper calibers are not needed to make hits at long range. I have hit a 2' diameter target at 1340 yards with a 308 (albiet only about 50% of the time-- the misses were unspottable).. and that's 3/4 of a mile. 1/2 mile is "only" 880 yards, which is well within 308's range (though I'd take my 260 over the 308 any day). There are a lot of calibers that can make it that far, but you need high BC values. At my altitude, 260, 6.5-284, 300WM, 6.5x47, 7RM, 388LM, etc, should all make it there provided the right load is used. Detecting hits from the smaller 6.5mm calibers may be difficult since they are not as audible on steel.
The last time we were shooting at a mile, it took both the 50BMG and the 338LM's present a shot or two to get the wind figured out, and then they were making hits. At 1340 (again, 3/4th mile), hitting a 2' diameter circle with the 338's was boring... well, until the wind changed again. At that distance, each 1 mph crosswind (averaged) pushes the bullet another approx 8 inches. It's easy to see how a very slight change in condition can yield misses.
-z