I bought my 1961 Magnum Twelve on line for $400 Canadian (= $340 US). Could have bought one a little nicer one for fifty bucks more. The problem with those old magnums is they are always full choke. Not much you can do with them but shoot trap. Barrels can be tubed by Briley but requires using their thin wall chokes. They used to charge $150 + $50/choke tube. Four years ago in Missoula pawn shop I saw a beautiful like new A-5 Light Twelve with MODIFIED choke for under $400. That is a pheasant killing machine! I told the clerk that price was a steal. "We've had it on the shelf for more than a year at $600."
Your gun is maybe good for parts. The receiver is ruined from pitting. If the wood is in good shape, that might help sell it. John and Val Browning should have changed the design so the stock was anchored through the butt instead of tang screw. Stocks tend to crack through the tang screw. Also, they should have sleeved the fore end with a steel tube so the barrel ring wasn't continually pounding the top end of fore end to pieces during cycling.
Here's my A-5 Magnum. I changed it to synthetic after going through two sets of wood. The barrel is 1990s Miroku with choke tubes. The receiver isn't cherry but not pitted. If someone wants to pay you $800 for that gun, jump on it. Personally, if you took it to a gun show I think you'd be lucky to get $300 ... and only if the wood is good.
Incidentally, everyone makes a big deal about the Belgian FN models being great stuff vs later ones made in Japan. The exact opposite is true. The Miroku guns were much better. They used more metal, came with choke tubes (none of the FN guns, A-5 or Superposed, had choke tubes), the bluing was beautiful, and they reinforced the fore end with more wood and later a cross bolt.
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