While the Brown Bess Musket fired a three quarters inch diameter lead ball (.75 caliber!), the colonists had much larger weapons, usually mounted on a carriage of some sort, be it at sea or on land.
The Amendment, however, was not ever intended to be in any way a limitation on arms by the people, and did not of itself grant any rights. Instead, it was a limitation of the power of Government, that Government SHALL to leave the Right to Keep and Bear Arms uninfringed.