Silver Bullet member
The stamp is not fully impressed so it is difficult to see at best. It looks close to the series 5 mark shown in Duncan McCollum's JAPANESE RIFLES OF WORLD WAR II but not completely. I have looked with a magnifying glass under all kinds of different lighting angles and the drawing is what one can see for sure. There may have been more at the bottom where the stamp thins out, can't tell. Any ideas?