Men in soldiers' uniform -- I would guess they're artillery uniforms, although I have no expertise in the matter -- well, they could well be disassembling a full-mounted Gatling Gun and reassembling it.
Although movies would eventually be used for instruction of soldiers, this is nothing of the sort. It is, instead, a precision drill team, carrying out a single military operation at high speed. Such teams would tour the country, either to recruit men for the army or, more commonly, as a novelty act, doing the same thing over and again at fairs or vaudeville houses. Some, like the Zouaves, with their wildly different uniforms and crack rifle drills, were popular for decades after the military units rose to prominence in the Civil War.