The other day I was just mentioning about some plastic or teflon pallet/slug. But I was thinking if such can be made in precision with lead core for weight it may serve a good purpose, in lesser air pressure one might achieve higher velocity. Teflon once locked into the rifling might glide smoother, with no carbon dust emission for subsequent shots, airgun has no firepower so heat may not be an issue. Come to think of ur barrel might even last forever!