It is a Japanese Type 99, the most common Japanese rifle of WWII and a popular souvenir for American troops. The circular stamp is the Chrysanthemum, or "mum", the "mon" or symbol of the Japanese royal family. The other characters read "9 9 Type". Rifles surrendered in Japan after the war had the "mum" ground off, a concession the U.S. made to the Japanese so they didn't have to turn over the imperial symbol to the recent enemy. Rifles with the "mum" intact were usually combat captures.
As to the rest of the rifle, some good pictures will be needed. Many of those rifles were "sporterized" in one way or another, so intact ones with the "mum" are fairly valuable.