The owner's manual, configuration and comparison with known examples.
They came in various barrel lengths and choke combinations. If it is not marked on the side of the barrel, you will have to pattern the shotgun to determine the choke
No way of knowing without a serial number /model number to identify what type of .410 gauge stevens you have.
It a Savage models ... 30D, 30E, 30F or Stevens model 67
Your serial number indicates that your Browning light twelve auto-5 shotgun was made in the year 1955.
1925
Frame
50-500 usd
Should be marked on the barrel
how old is the browning shotgun with the serial number 8G 12882
If you are asking about a Browning Auto-5 shotgun,then it was made in the year 1923,with the serial number that you have provided.
About $300, depending on condition, barrels, etc.
Any utility grade single shotgun in working condition is worth about $50 - $75. Would need more information to determine the age - exactly how the J. Stevens company name is written will get us close. There's nothing unusual about a break open single shot having an open hammer if that's what you mean by "cock like a hand gun."