OK, why not inlay blocks of matching wood (assume walnut?) after carefully routing out the existing checkering panels in a jig to form a flat bottom mortise? Glue in the new blocks of wood, leaving them well proud of the stock contours, then rasp down to shape and cut new checkering. Disguise the glue line with mullered borders. Finish to suit. Gun is probably not worth the effort, but it's good practice.