The US made 40% silver half dollars until 1970, right? The Mexico 100 peso series went from 1977-79, so that's a few years later. Is there any other issue which can beat that? I think some of the Mexico Libertads were technically legal tender at the prevailing silver rate, but they still weren't exactly regular circulation coins. For comparison, a 1980 Casa de Moneda 1 ounce silver round. This series was made from 1978 to 1980, so it actually coexisted simultaneously with the silver 100 pesos. Anyway, please post any circulating late (1964 and after) silver coinage if you like.