The US Model 1816 Musket was a .69 caliber

Caliber

In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

 flintlock

Flintlock

Flintlock is the general term for any firearm based on the flintlock mechanism. The term may also apply to the mechanism itself. Introduced at the beginning of the 17th century, the flintlock rapidly replaced earlier firearm-ignition technologies, such as the doglock, matchlock and wheellock...

 musket

Musket

A musket is a muzzle-loaded, smooth bore long gun, fired from the shoulder. Muskets were designed for use by infantry. A soldier armed with a musket had the designation musketman or musketeer....

 used in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 during the early 19th century.
The War of 1812 had revealed many weaknesses in American muskets. The Model 1812 Musket was created in an attempt to improve both the design and manufacture of the musket. The Model 1816 made further improvements, and replaced the Model 1812. The Model 1812 had borrowed heavily from the design of the French Charleville model 1777 musket

Charleville musket

The Charleville muskets were .69 caliber French muskets used in the 18th century.- History :Marin le Bourgeoys created the first true flintlock weapons for King Louis XIII shortly after his accession to the throne in 1610. Throughout the 17th century, flintlock muskets were produced in a wide...

, and this design was retained for the Model 1816.