12 has a bigger bore.
a 20 gauge is a type of many shotguns but it is smaller than a 12 gauge but bigger that a 410. a 20 gauge is a good shotgun for all ages.
These shotguns came in 20, 28, 16, And 12 gauge calibers
Rifles are referred to by caliber. Shotguns are referred to by gauge.
The gauge of a shotgun is directly related to the size of the barrell. In the cases of shotguns the sizes going from biggest to smallest for 'standard' (not all) shotguns is. 10 gauge, 12 gauge, 16, gauge, 20 gauge, and a .410 bore shotgun (410 is not a gauge but a caliber)
75-100 yrs ago
try: SAVAGE SHOTGUN.COM
20 gauge marlin ou 2 triggers
Utility grade made @ turn of the century