In actuality it's not that difficult to get 4 shots off (starting with a loaded rifle) in one minute. I can do this with either flint or caplock rifle's... Now I'm talking standing your ground, not running through the woods... Here's the thing in getting it done;
One must know exactly where everything is that you need, and in my case I don't have to go into my shooting bag at all. Outside my bag - my horn and powder measure is always in the same place, then my ball block with lubed patched balls, then my short starter, (ram the load home), then my caps are in a piece of hole punched leather for the #11 cap / and or - just prime from the horn (depending on which rifle you're using).
It's not hard at all if you stay to one loading routine with your components always in the same place.
I will admit that since I've grown older (like we all do) I've probably lost some speed in loading - but then if I'm starting with a loaded rifle - 3 shots in one minute ain't bad either.
Here's a good test; set a 100 yard TQ-4 NRA target out at 25 yards - and just see how many shots you can get off in one minute (starting with a loaded rifle - then reloading as fast as you can - your time starts at the word "go"). Don't worry about hitting the "X" Ring - just hit the target somewhere... The reason being - if you're having to reload and shoot fast you're probably in some kind of danger that's close to you and as "big as a man's bread-basket" so get a round (or two or three or four) into that target paper that is 14" x 14" square. If you can do 3 or 4 shots in one minute you probably have a good chance at surviving the reason you'd have to reload fast.