How many steps per minute when marching?

[RedRover]

This is another very interesting fact. It surprises me also. I would have thought that the interval between ranks was measured at 13" between RR Chest and FR Back, regardless of the presence of knapsacks, in order to be sure that the muzzles of the firearms of the RR Men would not be too close to the FR Men's Faces during firing. As the interval was, instead, 13" from RR Chest to FR Knapsack, then that was perhaps 5" more (the approximate depth of the knapsack) that was removed from the distance between RR Musket Muzzle and FR Face. And, perhaps, another 8" more (complete estimate) was removed when the men "T'ed" the feet, which pulled backward the shoulder, during the firing process. So, for a two-banded musket like the Harper's Ferry version of the 1855 Springfield Musket (which, I think, is the type that was illustrated in Hardee's Manual), with a total length of 49", the distance of the muzzle from the RR men's faces was not very large. I calculate:
13" Depth of FR Man + 5" Approximate Depth of Knapsack of FR Man + 13" Interval between FR and RR + 8" Shoulder Pull-Back During "T'ing" of Feet of RR Man = 39" Total Depth to be Spanned By Musket of RR Man. In the case of the afore-mentioned Harper's Ferry version musket, 49" in total length, this results in only a distance of approximately 10" from the RR Musket Muzzle to the FR Face. I know that, also, each RR Man steps slightly, 8", to the right in order to aim his firearm more safely and "centered" within the interval between the heads of the FR Men immediately in front of him, which perhaps creates a total effective separation of 12.8" (Pythagorean Theorem in order to calculate the hypotenuse between RR Musket Muzzle and FR Face = c^2=a^2+b^2 = 8"^2 + 10"^2 = Square Root of 164" = 12.81") but still this separation of FR face from RR Musket Muzzle seems a bit too near for comfort.
For a model 1861 Springfield, or the 1853 Enfield, each of which has a total length of 55"+, the distance from FR Face and RR Musket Muzzle in this scenario is a more comfortable 16"+ (or 17.89" via the 8" Step-To-The-Right).

The 13 inch interval appears to have been considered the minimum necessary for the rear-ranker to be able to reload his weapon, or otherwise conduct the manual of arms...

Hardee's 1862 Confederate edition notes:

175. When recruits are formed in two ranks to execute the firings, the front rank men will raise a little less the right elbow, in order to facilitate the aim of the rear rank men.
176. The rear rank men, in aiming, will each carry the right foot about eight inches to the right, and towards the left heel of the man next on the right, inclining the upper part of the body forward.

Makes it evident the rear-rankers is leaning forward a little, bringing his chest towards the right of his front-ranker's knapsack, and rear-ranker's gun-barrel is over the right elbow of his front-ranker, not over his shoulder as I've seen many reenactor's do.