Kid,
Just an idea. I do a good bit of genealogy research and I find that "family lore" is almost always based in fact but not necessarily "true" fact. Since Tom Mix and Roy Rogers were both cowboy celebrities and Roy was better know during this time frame, some one may have gotten them mixed up and changed the story some. This is never done maliciously it just happens as the stories are told and retold. Either way, you have a very cool gun. Congratulations and good luck in your research.