They were called "Greenie Stickem Caps" and were for the Mattel "Shoot'n'Shell" line of pistols and rifles. The Shoot'n'Shell revolver was the coolest gun ever.
I had a "Shoot 'n' Shell" gun for years that I wish I'd retained - remember the swing-out derringer belt buckle that you shot by flexing your tummy? Very cool...
