I found a couple boxes of the poly ammo and bullets in my stash, and they were fun to play with at limited range. They were marketed as the "Speer Target .44", and used only primers for propulsion, pushed in against a hard surface. Once spent, you could remove them with a nail. The bullets would cut a wadcutter hole in paper targets at modest distances, and the poly bullets could be reused.
Haven't seen them marketed in years; pretty sure there were lots of liability questions, not to mention how to handle a gun that was 'sorta' loaded. And now, with the price of primers, they'll disappear again in my junk collection.
Moon