To Carl,
Excerpt from Patent No. 14, 315, Fig. 1 as follows:
"My improvement consists in using fibrous material, instead of a flexible metallic one, and in expanding it into the scores of the gun by the explosive power of the. powder when ignited by devices hereinafter described. The best material for this purpose is hemp, spun or woven; but cotton or other fibrous material, or vulcanized India rubber, or strips of common rubber woven with gum or other fibrous materials, may be substituted with excellent effect."
Gutta-percha is also called India rubber.
Regards,
John