That's fast shooting. Don't let the anti's know these muzzleloaders are capable of that rate of fire! (I know that you meant minutes.)In my younger days I did try military cartridges loaded in military fashion . And have shot in a competition that way that way.
I watched Ted Spring ( writer of severe sketch books on F&I) get off 22 shots in a timed 3:45 seconds. British army requirement were for 15 shots in that time, one shot every 15 seconds 4 shots a min
As I said I was younger and fools do have good guarding angles some times.
Today I would Berber try it. Load, then prime at the line.
With blanks and the military style of reloading I have done 4 shots a minute. Three shots a minute is relatively easy, especially when no one is shooting at you.
I have shot muzzle loading rifle silhouette matches. Starting with a loaded rifle, you have 5 minutes to fire 4 rounds. Usually, even when measuring the powder charge, I got the 4 shots off in 3 1/2 minutes. In those matches, priming or capping was done as the shooter stepped to the line to fire. You do need to wipe the bore between relays to remove fouling and the crusty ring at the breech.
Hammer stalls are one of the few means to stop inadvertent firing. I have the scars on my hammer stall to verify that I have tested this practice even though at the time I didn't intend to perform that safety test.