Unexploded ordnance from WWII can be found in the US, literally in a persons backyard. A number of years in San Diego County several school children found an unexploded mortar round. Some of those kids were tragically killed when the round went off. It seems that the housing tract they lived in had once been a weapons range during the forties. The Association of Aviation Ordnancemen began giving lectures at schools to teach the kids the hazards and deadly consequences of playing with UXB's. Not sure if they still are doing it but it has saved countless lives in the San Diego area.
As a retired Aviation Ordnanceman I implore anyone who has a souvenir piece of ordnance from a small arms cartridge to things larger to have them removed from you residence. That "safe" dud can and will detonate after a while. As Ken Stallings states, dud and unfired ordnance will degrade to highly unstable compounds that are shock, heat and electro-magnetic sensitive. Here in Kern County California the Sheriffs Office bomb squad will pick up your grandads souvenirs with few or no questions.