The modern mad minute meme is basically folklore drift from the 15 aimed rounds of Practice 22. People just want to see how " well" they can do. I have seen some quite large numbers of rounds fired in a minute from a no4 or smle, but they are not practicable on anything other than the most perfect conditions- and usually not to the 1909 standards of accuracy. The Bloke on the Range managed 29 with an SMLE, but that was at 25 yds with quite a few fliers. Interestingly, he suggests that the difficulty of picking up target with open as opposed to aperture sights was a limiting factor.Indeed so but 15 aimed rounds in one minute with two reloads is very rapid work and very creditable but not the classic ‘how many rounds can you get off and hit the (variously specified) target in one minute ‘mad minute’ meme’.
FWIW my grandfather qualified on the Practice Number 22 and used his skills in 1914 onwards. I have failed miserably to equal this but fumble every charger reload. Now standing with my Martini Henry at 100 metres I could do 12 aimed rounds. Rather shows my my limits and the old boy would have gone a funny colour and shouted rude things at me very loudly had I the misfortune to be one of his soldiers. But then he learned his skills the hard way in South Africa.