This is a Prussian Model 1809 (Potsdam), possible Civil War use.

The Crown Proof Mark: in the barrel bands, i.e., Crown over styled Gothic/German letter is a "D". There are other inspector marks.

• Action & Conversion: The images show that the "pan" area of the lock plate has been ground down and the flash hole plugged. This is a classic "Belgian" or "Cone" conversion, where a percussion nipple was screwed directly into the top of the barrel.

Both the Union and Confederate Armies were desperate for infantry arms and purchased thousands of them, which Union soldiers called the "Potsdam Muskets". These rifles found extensive front-line service during the first two years of the war, until domestic production of Springfield or other domestic manufacturers could meet the demand.

• Caliber: The measurement converts to , which is the nominal caliber standard for U.S. infantry muskets of the early-to-mid 19th century.

The Barrel Length: You noted a 35" barrel.

The Ramrod: Having the original "tulip" or "button-head" ramrod

The condition is "Flayderman's Good," which typically means the metal has a smooth "plum" or gray patina, the wood has minor dings but no major cracks, and the markings are legible.