Just looking at the size and shape, and basd on dim memory. . .
they look like the cartridges that came with a special derringer mounted in a belt buckle, that when you puffed your gut out while wearing it, the derringer flipped out and fired, or you could dismount it and hand fire it. Single shot. I believe made by either IDEAL or MATTEL, and meant to use the round "Greenie Stick'em Caps" you'd stick on the round recess of the bottom of the cartridge.
I believe came out around the same time as the TV westerns like "Yancy Derringer" or "Bat Masterson" in the late 50's.
Man, if only I had some of the toy guns, rigs, etc. I had as a kid in mint condition still in the box.
I even had an entire Cavalry uniform with plastron front just like the kid wore in "Rin-Tin-Tin". "Yo-o-o Rinnie!"