about British musketry
A British officer wrote about the 1st Foots Guards at Dettingen,
They were under no command by way of Hide Park firing, but the whole three ranks made a running fire of their own accord. ... The French fired the same manner, without waiting for words of command and Lord Sinclair [the allied commander] did often say he had never seen many a battle, and never saw the infantry engage in any other manner.“
Muir page 77
This is confirmed by a lot of other sources, Beerenhorst for example
„The 88th next deployed into line, advancing all the time towards their opponents, who seemed to wait coolly for them. When they had approached to within three to four hundred yards, the French poured in a volley or should I say a running fire from the right to the left. As soon as the British regiment had recovered the first shock, and closed their files on the gap it had made, they commenced advancing at double time until fifty yards nearer to the enemy [but still at least 250 yards away], when they halted and in turn gave a running fire form their whole line, and without a moment’s pause cheered and charged up the hill against them.
Muir page 82 (33)
(Costello, The Peninsular and Waterloo Campaigns, p. 125)