A English and Indian Brown Bess is a .75 caliber normally. Many of the old military flintlock muskets were extremely large bore. Common were .69 caliber. There reason was since the things were not accurate at long range, they wanted to inflict a large wound. Also the style of fighting they did in volly fire, they might shoot at you and hit two men down the line. And that big roundball would go through one person and chances are wound someone behind...