It's hard to see small details in the posted images. It would help to see closer pictures of the lock bolt washer, tang, guard & triggers, and rear pipe. One possibility, although a swag, is Samuel Switzer. He was born in PA, worked as a gunsmith in NY in the 1840s, then moved to Fountain Co., IN, in the 1850s. The reasoning behind this possibility is the good lines of the rifle (PA exposure), but also the lock bolt washer that's a NY perc. era style. However, I've never seen his earlier engraved initials/signature, just his much later stamped signature out here in the Midwest. May not be your man, but his background matches the style, and his NY years "kind of" match the lock bolt washer, in the 1840s he was close to NJ where gun was found, and the initials fit. So now someone needs to find a better fit!
Shelby Gallien