MIKE GEORGE says: Nikko shotguns were made in Japan, and are no longer in production. The last guns came into the UK during the early 1980s.
The most familiar model was the 5000, which came in field, trap and skeet configurations. As far as I recall, there was no sporter.
The guns were quite well made and handled well, but the fault was, with long use, the ejectors could become splayed outwards to the point they eventually over-rode the cartridge heads.
At best, this gun is going to be around 25 years old, and with a gun no longer in production there is an obvious spares problem. If anything breaks, you would have to be prepared to pay to have a one-off part made. If you are still tempted to buy, I suggest you get it thoroughly checked by a gunsmith before you part with any cash!
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