Some things never change. Since the firearm became the standard weapon of the infantry, and it ceased being a pike that could fire a couple of volleys, it’s been about a meter long and weighed about 4 kilograms — call it a yard and nine pounds on the English system.
Sure, the guns that are contemporaries are very similar in size, weight, caliber and effect, because they’re shaped by the technology of the day, but why should a new gun be proportioned roughly like one of two centuries ago?
Because that’s about what a man can conveniently carry and manipulate in combat, while executing foot maneuver under enemy observation and fire. So that weapon size is a natural size, dictated by biology as much as anything.
For as long as recorded history has been written, the fundamental unit has been about 100-150 men. Here’s a British wargame guy explaining how that’s a natural size, dictated by biology — neurological and social biology perhaps.
Can you think of some other examples of weapons sizes, shapes and performance envelopes that are defined, one way or another, by the limits of human biology?