Re: Need help identifying riffle.
It is a late war Type 99 Japanese rifle. The bolt is missing its internal parts (firing pin, spring and safety). Very often, veterans with children disabled souvenir rifles to prevent accidents.
It looks like the Japanese imperial crest, the chrysanthemum, has been ground off the receiver ring, which most likely means your grandfather got it from a depot in Japan rather than in combat. As a late war rifle, its value is relatively low, and the missing parts make it worth less. By coincidence, I saw a rifle almost like it at a gun show today; it was also missing those parts, and had a price tag of $150. It didn't sell when I was there, so I don't know whether it sold or how much the seller got for it.