Oriental Single shot Shotgun Info

My son has just come into a long arm rifle. Upon examining it, it is a smooth bore barrel which is a shotgun. The weapon has oriental markings on the headstamp, has a rabbit ear hammer, and a pivot breech to load a single round. It appears to have some age to the weapon due to the wood being dark colored. There is not a numeral for the gauge or serial number anywhere visible. we did not take the wood off yet.

I can not post any photos, being a new member. Any information is appreciated. The weapon does not appear to be military and appears to be a 20 gauge in size.

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