I think it would work if it was kept in a hardened paste form and retained in the neck of the cartridge case, like a card wad.  If you put it loose on top of a full charge (for hard-cast bullets) of smokeless, maybe 1600 fps, I think you are courting danger. 

There is a lot written about damaged "ringed" chambers in original single shots, even with barrels made by Winchester and Remington.  The problem stems from over-powder wads, stuff like Dacron.