The Winchester 101 model is a shotgun that began manufacture in 1959. The gun originally was issued as a 12 gauge in 1959. Serial numbers for this model range from 50,000 to more than 140,500. The gun is also manufactured as a 20 gauge, 28 gauge and .410 bore.
The 20-gauge version of the Winchester 101 was introduced in 1966. The 28-gauge and the .410-bore versions were first released in 1968. Serial numbers for the 20-gauge, 28-gauge and .410-bore versions of the Winchester 101 start at 200,000 and move upwards over 228,500. Serial numbers for Winchester 101 model guns manufactured after 1971 may need to be verified directly with the Winchester Repeating Arms Company for authenticity.