1996
Sorry- no public published data for these.
These were made many years ago, and may not HAVE a serial number. Serial numbers were not required by law on rifles and shotguns until 1968. Yes, it is perfectly legal to own a firearm that never HAD a serial number IF the law did not require it at the time the gun was made. It is illegal to remove any serial number from a firearm, or to possess one that has had the SN removed.
To answer that question, we will need to know the date "code" - there will be a two letter code stamped into the left side of the receiver, usually found just before the serial number.
The Thompson Contender with a serial number of 7000 was made in the year 1967. Thompson/Center Arms is a firearm company that is based in Rochester, New Hampshire
$100
200
In answer to part two of your question, you usually cannot get a new barrel with the same serial number, however; the part of the firearm that must have a serial number is the frame of the firearm. In other words, a replacement barrel with a different serial number is kosher. Many firearms manufacturers will replace the barrel with a new one that has the old serial number along with additional numbers/symbols/letters to indicate it is a replacement as long as you send it to the manufacturer for repair.In answer to the first part, maybe. Without knowing how bad the pits are, and any other possible problems you might not see, it is not possible to give a definitive answer on you case. Consult a gunsmith.There are very few firearms that are serial numbered on the barrel to match the frame/receiver. There is no requirement to have a number on the barrel.
I can say that the new england brand of shotguns were imported between 1987-2007.These were imported by H&R.
I do not know of any location that has NEF serial number data for dating this shotgun. NEF made/makes relatively modest priced firearms. You could be in the 50-200 USD range depending on model, papers, accessories, etc..
Made 1989 to date, sold for about $150 new, No serial number data published.
new haven model number 4958 serial number 427569