@WebleyGreene455
Since I'm also kind of an antique knife nut, been doing a little follow up research on the Quigley knife/knives and poking around in some of my "Bowie knife" references. Yes, you are absolutely correct, the handle looks to me like a solid section of NA elk antler. What is curious about it is the overall design. Most movie props are a compilation of whatever is available and "close to period correct". But this may very well be a knife owned by Selleck at the time or provided him by a custom maker for use in the movie. Selleck has always been particular about his movie guns and accoutrements and has used much of his personal collection in some movies. His main knife looks to be a hybrid design... between maybe an1860 Sheffield "Bowie" and a much earlier late mountain man era (1820-40) "Bowie". Also note his boot knife has features resembling some of the early trade knives but in a much fancier form. The main knife's sheath is definitely earlier mountain man era -X- later Bowie with the designs and beadwork.
And as an aside, I too like the idea and looks of a "wedding band" spacer between handle and blade. Even some early rifle makers used that feature to dress up their guns, adding a decorative ring at the breech end of the barrel.
IMO, the Quigley knife blends an early design, the solid antler section handle, with a later blade design. The flat ricasso section, the hollow ground main edge and the fairly long false edge all point to a later blade design. But hey, the movie is set in 1880, so most earlier guns, knives would be correct.
Here's a couple of pics: one of the very old knife posted earlier with the antler slab handle and showing the detail of the faceted decorative band and the Quigley movie knives courtesy of, I believe, James Julia Auctions.
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