Your best bet would be to take it to a gunsmith for a professional appraisal.
70-100 years
Nitro in the name would imply smokeless powder, so the earliest would be shortly after 1900. Could have been as recent as 1945.
This would be a 12 ga. BPS (Hunter model) pump shotgun made in 1984
I would say that with the serial number 1321XX,we are looking at your shotgun being made by ithaca(who made the lefever nitro special) in 1924.
Assuming you're talking about who the company transitioned into, and that would be Savage Stevens firearms. http://www.savagearms.com/
Assuming you're talking about who the company transitioned into, and that would be Savage Stevens firearms. http://www.savagearms.com/
To get a parts breakdown you would need to take the shotgun into a gun store. The store will be able to provide an estimate, or order new parts.
nitro as it will get a better boost
Any nitro, ranging between 5% and 30% nitro. Anything more would clog the engine.
Gun shop, pawn shop, want ad, for sale ad, hunter, collector.
The 12 gauge King Nitro number 3411 is likely a vintage shotgun manufactured by King Nitro. It may have a 2 3/4" chamber and be of good quality, but specific details about its features and history would require further research or inspection by a gun expert.