There is confusion in identifying your shotgun, because the real William Moore made fine collectible English shotguns (percussion) until around 1899. These hammer guns are normally marked Wm Moore & Co., or with the full name of William Moore.
To capitalize on the name identification, Folsom / Crescent Arms later made a cheap shotgun using the "Moore" name. If yours is full of British proof marks it is an expensive piece. You can also see if it says "English Twist" on the barrels.
If yours is a Folsom copy it was made in late 1800's and early 1900's and has little collector value. They are mostly wall hangers, or worth around a $100.00 to someone who loads black powder ammunition. If you have Belgium Twist Barrels, or damascus it is a Folsom gun and must be inspected by a gunsmith to see if it is safe to use, even with black powder. The solder used in twisting the steel will rust and weaken causing a catastrophic coming apart of the barrel with fired. Be safe.
j'ai trouvé sa sur le net
en gros y dit qui a deux type le moore and co qui est vieux et le moore qui est une copie, le premier vaut plus cher que le 2e