It's a Mattel toy revolver "Fanner" made probably in 1960s. It uses shells and caps for effects, somewhat similar to what later became basis for Japanese modelgun industry. Note that pictured shells do not have "bullet" tips". Paper caps did not go inside the shell, but were stuck on the bottom, where hammer hit them directly. https://www.youtube.com/watch?v=hR9ojNddiSI