Did colt make a brass frame 1851?
I know the condererates military made or had made Brass framed guns but I was not sure they made 51 Navy models. I could be wrong.
The grips also look to be a different wood than walnut, but that could just be the picture. But it looks like a kit gun from the 80's And unless it was in soft clay I would expect there to be less of the gun. The nipples still look to have a hard edge.
Get a picture of the barell. That will tell if there are any proof marks from Italy.
My 1860 Colt cpoy has Italian Proof marks on the right side of hte barrel and on the left it says Black Powder 44. If it is real and not a copy it would not say black powder as Nitro powders were 30 years away.