I believe that this Samuel Morrison is the same Samuel Morrison who appeared in Pekin, Tazewell County, Illinois in the early 1840's and died there on April 1, 1850. I might have completely overlooked him if it had not been for an ad, placed by his successor John Schultheis, in "The Tazewell Mirror", Pekin, Illinois, dated April 11, 1850. It stated that he had "taken the shop lately occupied by Samuel Morrison, deceased", and that he was prepared to repair old guns and make new ones to order. Samuel Morrison's estate file contains local bills against his estate dating as early as April 24, 1841, and referring to him as a "gunsmith". Morrison owned house and lot 13, in block 38, in the city of Pekin. He also still owned land in Pennsylvania at the time of his death. Apparently anticipating his imminent death, Morrison sold his shop to Schultheis on February 18, 1850. Morrisons wife's given name was Maria, according to his estate file.
I have photos of another rifle, stamped simply S. MORRISON, that has a completely different type of mule-ear lock, this one being a "back-action mule ear", which I can send.