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“... The .69 caliber was probably preferred because a one ounce ball will mic out to be .69 caliber (16 gauge). ...”

16 gauge corresponds to a bore size of 0.662 inch. 0.69 inch corresponds to a bore size of 14 gauge.

Modern users (often reenactors) load French pattern muskets with various ball diameters, usually 0.68 inch or smaller.

An undersize ball was essential to sustained fire.

Continental Army ordnance regulations specified a ball diameter of 0.627 inch for French pattern muskets: plenty of “windage” - empty space - to enhance ease of loading even if the musket bore became fouled after several firings. Specified charge weight was 187 grains of powder: enough to prime the pan, while reserving enough for the main charge to give the loose-fit ball a pretty healthy initial velocity.

An undersize ball was essential to sustained fire. Very good, that's right. The early resolution of the continental congree required: "That each Soldier be furnished with a good Musket that will carry an ounce ball, with a bayonet, steel ramrod, worm, priming-wire, and brush fitted thereto; a cutting-sword, or tomahawk; a cartridge-box that will contain twenty-three rounds of cartridges, and twelve flints; and a knapsack.

See: http://lincoln.lib.niu.edu/cgi-bin/amarch/getdoc.pl?/var/lib/philologic/databases/amarch/.5533

Do you think that the requirement for a one ounce ball suggests the Continentals preferred the .69 caliber, of there was just a lot of sloppy shooting?