They were in production for I believe three years.I believe I've read here they were discontinued pretty quickly because they liked to come apart and wedge themselves in the barrel. You're looking at 50 year old hulls, not worth the risk of messing around with.
I really don't know but ,I was given a big container of them with the boxes and I don't remember anything on the box indicating they were loaded with nickle shot. But that was a long time ago .Got some around somewhere that have yellow printing on them. It signified nickel shot from what I was told.