I recently visited the National Museum of American History in D.C. and they had several Revolutionary War era firearms on display. I noticed that the rifles were of surprisingly large caliber .75, .81, and even 1.5! I know that these soldiers (judging by the size of the uniforms displayed) and humans in general were smaller in stature at the time, how were they able to wield these rifles without destroying their shoulders? I'm 6'2 250lbs and can barely fire a .50 rifle while standing, am I outing myself as a wuss or was there a certain technique to it?
While I cannot say much on the weaponry of the American Revolution, I can talk about muskets and rifles.
Generally, calibres are larger in the 18th and 19th century. A French Charleville used a .69 calibre ball while a British Brown Bess used a .75 calibre musket. The reason 'smaller' men were able to fire lager calibre is the strength of the powder. While I don't have hard math to back up the power of black powder, it was much weaker than the current smokeless powder. However, to put it perspective, a standard musket with a measure of powder has an effective range of about a hundred meters. So, it isn't exactly the calibre that you should consider but rather than technology (black powder).