Mike,
I did some digging a while back on Simon. Here is what I have so far....
Joseph J Simon was in Chicago in 1880 working in a "car shop". He is listed as Bohemian by birth. I assume a couple of things. "Car Shop" is referring to street car, where he was possibly a mechanic or some one who cleaned the cars.
He lived in Illinois until at least 1885, his daugther Elizabeth was born in Chicago. By 1899 he is in California where his daugther Gladys is born.
The 1890 census data is not available.
In 1900 Joseph J Simon, Austrian by birth, is working as a gunsmith. His son, Joseph F Simon is working as a clerk for Wells Fargo. Is there a connection here? I am not sure....
The nationality changes reflect the changing map of Europe.
I can not find Joseph J in the 1910 or 1920 census. However, I do find Joseph F living in San Francisco working as book keeper.
So the output of Joseph J Simon as a gunsmith has to be very limited. JH Cummins only shows so far in 1900. He was a "capitalist" who went to Hawaii. His wife was born in Portugal.
Simon in the 1900 census
Cummings in the 1900 census
Given the above, it would be logical to assume the gun dates between 1890 and 1910.
However, I do not know the actual maker. Here are some pictures that may help.
Pete