Cannon Recoil!
I was amazed to see, in The Horse Soldiers, that the cannons jumped back with realistic looking recoil when fired.
Over fifty years of movie watching, I have come to accept that in movies, cannons are not shown to recoil, regardless of what era is being depicted.
I realize that if you show cannons in a realistic war setting, it will be almost imperative to use blank ammunition, which doesn't make the gun recoil.
The first couple of times in THS that cannons fired, the camera shot did not include the whole gun. I can think of various ways the gun could be made to move back, but they involve something visible to pull it.
In the last cannon firing, the whole gun could be seen in the camera frame, barrel, wheels, carriage and trail, and . . . . it moved when fired!!