Hello...what model do you have?
I'm sorry the first expert was not able to give you an immediate answer but I can assist you. This a Beretta Tricentennial "1680-1980" Commemorative Model M1000, 12 ga. black powder muzzleloading percussion over/under shotgun. Mfg. 1980 in Italy. This is a rare and unusual shotgun. One of only 300 guns produced in 1980. Very unique and showy looking piece! 30" over/under browned finished barrels with ramrod on right side. Hand-engraved lockplates, hammers, trigger guard and tang that are also nicely case-colored. Walnut stock with left cheek piece and case-colored buttplate. Two engraved and case-colored barrel bands. Light engraving on barrel and is marked: "1680 Pietro Beretta Gardone 1980". Unique three-piece forearm section that is beautifully done. Brass front bead sight. It should look like the image below:
With the gun still in the box in unfired condition the value would be in the $2100-$2350 range. The higher end would be to a private collector and the low end to a gun dealer who will resell it.
If you need further assistance let me know. Otherwise please accept/rate my answer in order to close the question out.