Post a pic or accurately describe all markings on the weaponand the overall length, length of the barrel, style of the stock etc.

I'd be willing to bet someone here will be able to identify the make and model, ... but as for the chambering .. unless it is clearly marked you will be guessing .. and even if clearly marked the chamber could be "cooked" enough that it is either not safe or will never throw a 10 inch group again.

A chamber cast is your best and most prudentbet.