A nice set.
James Nosworthy was a "hotel hunter" for the Great Northern Ralway which was founded in 1881 being reformed out of other railroads. A Wki cut-and-paste:
In 1867 the Minnesota & Pacific Railroad was chartered to build a line from Stillwater, Minnesota, on the St. Croix River east of St. Paul, through St. Paul and St. Cloud to St. Vincent, in the northwest corner of the state. The railroad defaulted after completing a roadbed between St. Paul and St. Cloud, and its charter was taken over by the St. Paul & Pacific Railroad (StP&P), which ran its first train between St. Paul and St. Anthony (now Minneapolis) in 1862. For financial reasons the railroad properties were reorganized as the First Division of the St. Paul & Pacific. Both StP&P companies were soon in receivership, and the Northern Pacific Railway, with which the StP&P was allied, went bankrupt in the Panic of 1873.
In 1878 James J. Hill and an associate, George Stephen, acquired the two St. Paul & Pacific companies and reorganized them as the St. Paul, Minneapolis & Manitoba Railway (StPM&M). By 1885 the company had 1,470 miles (2,370 km) of railroad and extended west to Devils Lake, North Dakota. In 1886 Hill organized the Montana Central Railway to build from Great Falls, Montana, through Helena to Butte, and in 1888 the line was opened, creating in conjunction with the StPM&M a railroad from St. Paul to Butte.
"In 1881 Hill took over the 1856 charter of the Minneapolis & St. Cloud Railroad. He first used its franchises to build the Eastern Railway of Minnesota from Hinckley, Minnesota to Superior, Wisconsin, and Duluth. Its charter was liberal enough that he chose it as the vehicle for his line to the Pacific. He renamed the railroad the Great Northern Railway (GN); GN then leased the StPM&M and assumed its operation. Hill decided to extend his railroad to Havre, Montana, west to the Pacific, specifically the Puget Sound at Seattle, Washington. He had briefly considered building to Portland, but it was already served by the Oregon-Washington Railroad & Navigation Company and the Northern Pacific Railway (NP)."
I think "firearms historians" look at the 1863 dated accoutrements and the GN Railroad being formed after 1881, and want to say that Nosworthy commercially hunted with his muzzleloader at that time (rather than say something more modern).
The belt set sold for $800.
It looks like the belt itself is a British rifleman's "snake buckle" belt.
And the whistle is listed as a 'dog whistle."
The .50 plains rifle was made by Philadelphia gunsmith William Robinson likely before 1845. Robinson was briefly partnered with the more famous John Krider 1837-1838...and then went on his own in 1839. Robinson disappears in 1845. Krider went on as a famous rifle, shotgun, and pistol maker. He went on to establish the "Sportsman Depot" a fore-runner of Gander Mountain or Cabelas.