Post WW2 through the 1970's.
when was the carolina arms 16 gauge single barrel shotgun made
1901 single barrel shotgun, washingtion
How much is a 16 gage single barrel shotgun model 350A Revelation
An early model Lefever single-barrel 12-gauge shotgun with a 30-inch plain barrel can be found for sale online for $300. This is the price for one that is in excellent condition.
Numerous companies in many countries have made single shot 12 gauge shotguns.