5000 and 5100 were action types, used on a number of different Springfield and Stevens guns as well as numerous "trade brand" guns such as Eastern Arms Co. The 5000 and 5100 action types were introduced in 1936, replacing the old G.S. Lewis design action used on many Stevens, Riverside, Springfield and "trade Brand" guns from before WW-I. From parts lists it appears that the main difference between the 5000 and 5100 were a bit of action profiling and the top-lever and spindle. With the introduction of the new actions, the Stevens No. 330 became the Stevens No. 530, the Springfield No. 315 be came the No. 515, and very briefly J. Stevens Arms Co. made an entry-level Skeet Gun the No. 500 --
For 1940, J. Stevens Arms Co. introduced their Tenite stocks and forearms on a variation of the 5100 action, and called the gun the Stevens No. 530-M --
This gun was offered through 1946. As Savage Arms Corp. consolidated their arms making operations at their old J. Stevens factories in Chicopee Falls, Mass. after WW-II, this Tenite stocked 5100 action gun was called the Springfield No. 311 in the 1947 Savage/Stevens/Springfield/Fox catalogue --
By the 1948 Savage/Stevens/Fox catalogue it was called the Stevens Model 311 --
The Tenite stocked gun was offered through 1950, but by 1951 it got a wood stock and became the Stevens Model 311 most people know.
Also, back in 1940, Savage took the internal parts of the 5100 action/Stevens No. 530 and put them in a somewhat nicer profiled receiver, with a bit nicer wood and checkering, and introduced the Fox Model B in their 1940 A.H. Fox catalogue.
If the gun in question was made 1949 or later there will be a small oval on the bottom of the receiver, just back of the forearm iron with a number and a letter, beginning with A=1949, B=1950, etc.
Many of the pre WW-II Stevens/Springfield doubles had serial numbers, but the records are long gone and even the Savage Historian can't give you a date.