In traditional rifle match shooting, 200-600 yards are considered "mid range", and 800, 900, and 1,000 yards are "long range". That said, most shooters would consider 600 yards pretty damn far away. Any real hunter would consider that too damn far away - that places one well outside the sensory perception of the target animal and in no way pits the hunter's wit and skill against the animal. But I digress...
My "long range" experience is almost purely with the black powder cartridge rifle. When I first started shooting these matches, we were all shooting our favorite rifle chambered in the .45-70 (also known as the .45-2.1"), utilizing duplex charges of smokeless under black to achieve the necessary velocities. Later, as the game took off and brass and dies became available for other chamberings, I went to the .45-2.6", or .45-100 with straight black powder, for long range work.
Here are my two "long range" rifles. You will note there are no scopes on them. There is a scope class, but us iron sight guys usually beat them. With the very distinct, very visible official NRA target, even at those ranges, a scope is not required to shoot well. Top photo is an 1875 Sharps from C. Sharps Arms in .45-70, bottom is an 1874 Sharps from the same company in .45-2.6". Both wear #1 heavy 34" full octagon barrels and MVA spirit level globe front sights.
I will tell any erstwhile rifleman that if you ever get the chance to shoot at long range, on an established range, do not pass it up. It is a learning experience that you will never forget. It doesn't even matter what you bring, what glass is on it (or if it even has any), what it is chambered in - none of that. Just go with what you have. If you subsequently get bitten by that bug (and I sure did), you have plenty of time to put together a dedicated long range rig. Decide what you want to do - compete or just target shoot, antique or modern - there is a wealth of knowledge out there to get you on the right track. Be aware, though, this gets expensive fast. If yours is just a casual interest, just use what you already have.