I have seen a number of original rifles with no buttplate. Why are they not worn excessively?
Not having seen the same rifles, and not knowing what you would consider to be excessive wear, I can't say for sure. In general though, end grain of woods typically used for gunstocks (maple, walnut, etc) is more resistant to abrasion and fracturing than is horn.
First off, horn is soft. It is particularly susceptible to abrasion. I've seen the heel of a horn buttplate worn almost to the underlying wood after a single season of match shooting (and since it was on my rifle, and I was quite fond of the horn buttplate, I paid a lot of attention to it). Granted, that season probably consisted of close to a thousand rounds in competition plus an equal amount of practice, but none of the other components of the rifle were worn out, and brass buttplates that received an equal amount of use did not show the same wear.
Second, relative to other materials (including bare wood) commonly used for buttplates, horn is particularly susceptible to shock: if the butt of a gun hits a hard object, it will sometimes crack. Other materials crack too, but not with anywhere near the same frequency. Horn used in applications like a buttplate will also sometimes "fray"--almost like the end of a toothpick that has been chewed so the fibres separate. This tends to happen around the edges, and then the loose fibres get broken off, and it begins again.
It isn't like a powder horn getting bumped into objects--most powder horns weigh less than two pounds, and while they get bumped on stuff, they can usually "bounce" away from whatever they hit. A buttplate is sandwiched between the weight of the rifle and a typically-unmoving object every time the gun is loaded.
In the last quarter of the 19th century/first quarter of the 20th century, horn--particularly pressed horn--was a common material used for buttplates on shotguns. It was cheap, it looked good when new, and it had a certain "old world" image. They also had a reputation for being fragile and showing wear within a short period of time--and this was on breechloaders, not ML guns that are stood on the butt to load every shot.
Yes, there were guns made with horn buttplates, and horn furniture, back in the day. They tended to be guns for show, or to be owned by the well-off, who often had attendants to care for and even load the guns for the shooters. If you're building a safe-queen or display rifle, why not use horn? It does look good. But for a working rifle, there are better choices.
