US Model 1816 Flintlock Muskets dated 1823 through 1832 are called Type II Muskets. More of this type were made than the Type I and Type III. More Type II muskets have survived in their original flintlock configuration than surviving Type I and Type III combined.
Per Ordnance Department specification, all of their iron components, except their ramrods, had what modern day collectors call the National Armory Brown finish. All of the external lock components, except the battery(frizzen) spring, including the lockplate had a color case hardened finish. Internal lock components, bridler, tumbler, sear and all screws had a heat blue finish. The mainspring and sear spring were polished bright.
In 1828, the triggerguard bow was redesigned to have a full radius boss to which the rear slingswivel was riveted. Additionally, the Guard Bow is now riveted to the Guard Plate.
For more detailed info on Model 1816 muskets and photos see my article in Man at Arms Magazine Vol 42 #4 August 2020 or pages 68 through 100 of my book kindly posted by Dennis Glazener in the Recent Books section of this forum in August 2019.