There is no doubt about where this rifle was made, it was definitely made in St. Paul, Minnesota. The 1860 census lists William Golcher as a gunsmith in the 2nd Ward, City of St. Paul, Ramsey County, Minnesota. Wm. Golcher was 26, born in England. He owned real estate valued at $400; personal estate valued at $1,000. His wife Kate, was 23, born in Ireland. A daughter, Mary A., age 4, was born in New Jersey.
William Golcher is also listed there as a gunsmith in the 1870 census, age 36, born in England. He by then owned real estate valued at $20,000 and personal estate valued at $10,000. His wife Catherine was 33, born in Ireland. Their daughter Mary was now 14, but listed as having been born in Minnesota. Three other children, Nellie, age 9; Harry, age 7; and "Baby" age 6/12, were all born in Minnesota.
I have not been able to find the partner named Simpson.