My bet is on rice or a similar grain. Wheat does not have smooth edges and is rather square ended with spikes. This is a patch box beyond all others. Wish we could see more of the rifle itself, and maybe someone can get photos of it at the coming show. Also, who made it, where was it made, when was it made? Lots to consider here. Many thanks to you for posting the
photos here and giving us a glimpse of a pretty fantastic rifle.
Dick