There was a study years ago about Rev War era rifles and most were in the 50 cal. range. As Crow Feather mentioned, the caliber result using the same equipment would came out differently because they the barrels were made by hand forging.
That involved heating up wrought iron and hammer welding a flat piece of iron around a mandrel - by far the most laborious part of the process. Then the mandrel was removed and the hole was reamed to make it straight and round. Next came the rifling stage, which was another laborious process. At the end of that, the gun maker would make a ball mold to cast the lead ball that would fit that particular rifle. A .50 cal. mandrel could result in a .50 through about a .55 caliber rifle and anywhere in between.
The cost of a rifle was equal to a longhunter's yearly income from harvesting deer and working his farm. So you had to be very wealthy to have more than one rifle. Now, if you're going to only have one rifle, are you going to make it a squirrel gun? Probably not when that rifle was being used to feed and protect the family.
And if you were in Virginia, you may very well use it for 6 to 9-months out of the year to harvest deer for deer hides that were being shipped back in a rawhide state to England. They finished the tanning in England and turned them into very soft clothing, which was quite the rage in England and Europe until the Rev War started. Deer hides were the #2 export from Virginia behind Tobacco until the war started and shipments to England ceased.
Also, bear in mind that American longrifle calibers were much smaller than the smoothbore fowlers and muskets of the time. So although they sound large to use, they were small by comparison to the common firelock found in New England. Typically the fowlers were from .62 to .75 caliber (20ga. to 12ga.). Fowlers were commonly used in New England because you could take deer, squirrels and fowl with them - a real "all-around" firearm. Limitation was range and accuracy.
The first rifles that showed up in America were the Jaeger rifles made by Moravians who had immigraded from Germany. These Jaeger rifles were typically around .62 caliber or so. So even a caliber in the .50 neighborhood allowed you to make a LOT more round balls out of pound of lead than the muskets, fowlers, or Jaeger rifles did.
After the Rev War as you get into the late 1700's and early 1800's is when the calibers really started getting smaller and you saw a lot of .45 and .40 caliber rifles. A .45 rifle could still take deer reliably although a .40 depended a lot on proper shot placement. That's why modern deer hunting regulations in most states require a minimum .45 cal rifle to hunt deer. Another driving force is that the Eastern Bison, started disappearing from the Eastern US around 1730 and disappeared during the 1770's, so you didn't need the larger calibers to hunt them...they weren't there anymore.
No longer needing to shoot at targets that were shooting back at you with .69 caliber lead balls, and the reduction in the size of game such as the loss of the Eastern Bison had a lot to do with the reduction in size of rifle calibers over those years. Economy of use also had a part to play, but lead was easily available throughout the War and rifles already got a lot more round balls out of a pound of lead than muskets did. Rifles stayed expensive until Remington invented the barrel drilling machine in the 1840's that could consistently turn out identical rifled, straight barrels and even then they weren't cheap.
Twisted_1in66
Dan