I believe the hard rubber grips and other products such as mid-1800's bowling balls were made from a material known at the time as Vulcanite then, later to current,
Ebonite. Ebonite is a compound of natural rubber, sulfur, linseed oil and other fillers such as zinc oxide that was created by Charles Goodyear during his development of the latex vulcanization process. It was called ebonite because they wanted to use it as a replacement for ebony wood.
Gutta-percha, another source of latex, was also used to make handgun grips. So, people who call the material that 19th Century grips are made of gutta-percha aren't wrong. Calling them Bakelite
is wrong because it wasn't developed until the 20th Century.
I see Gary was posting as I was writing.