there are no dumb questions.
Your gun is definitely a Prussian M 1809 UM, made 1837 as a flintlock musket in Neisse, converted to percussion. You will find the conversion date on the underside of the barrel (on the upper - visible- barrel side is the flintlock date 1837 that corresponds with the lockplate date). Near the conversion date is presumably a letter marking showing in which factory the conversion was performed (if you find it I can tell you the factory).
Prussia introduced the percussion system in 1839 with the M 1839 smoothbore musket with patent breech screw ("Patentgewehr"). Also they began with the conversion of the flintlocks (not in 1831!).
The LWR/FW marking is exactly what you wrote. The number 165 is the (Prussian) gun number in the unit (not a Civil War number). On the guns are several markings, most indicating inspections. On some Neisse guns you can find on the lockplate a small script "S" under "Neisse". It is believed that this stands for "Schnackenberg", when the Royal armory of Neisse was under commercial administration of Mr. Schnackenberg for some time. The only American mark I know is the "City of Philad./Wurfflein" mark on some 1809 UM.
Best regards,
Marc