Actually, correctly configured, you can reload a bolt action rifle incredibly quickly - check out how the British Enfield rifle works. And with proper training, you can keep a pump action shotgun or lever-action rifle firing almost constantly, you don't run it dry, pause to reload, then continue - you reload in progress.
I have a US military assault rifle from 1874. It is a single-shot rifle, each new cartridge must be loaded in by hand. I can fire an honest 45 rounds a minute from it, until I run out of ammunition. It can put a bullet through 3 inches of oak and 8 inches of sand backing at 3500 yards. A bullet roughly 7x the weight of the bullet the AR-15 typically fires. At the Second Battle of Adobe Walls, a man was dropped at ~1500 yards by a shot with one of these (or something very similar).