It may not be possible, other than a general range of years. There in no listing for Neumann and Company in my references, There were millions of inexpensive shotguns made n Belgium from the late 1800s to early 1900s, and there are no records on most. A gunsmith may be able to identify roughly when from the proofmarks stamped on the gun, but that is a maybe. Sorry-
By the serial number.
Another Belgian shotgun. Neumann Bros were in business into the 20th century, although a gun that year of manufacture is doubtful. Value is going to be minimal, and the gun should be looked over by a gunsmith to ascertain exactly what you have.
You must indicate shotgun or rifle and model.
There is one shotgun. It is Belgium made. DePose POUDRER VIVE with name NEUMANN FRERES from LIEGE on barel. If You have some interests, please write on e-mail: viesturs_a@inbox.lv
your browning auto-5 shotgun was made in 1926.
Your shotgun was made in the year 1961 with a prefix of 1G.
Impossible to answer without the serial number.
your browning auto 5 was made in 1922.
1971
Your question cannot be answered without you providing the name of the maker of your shotgun,and then we can determine if there is any public data to identify the year of manufacture.
This gun was made in 1961.
You have a magnum 20 gauge auto-5 shotgun that was made in the year 1967.