This is all very interesting......
I have used the term riflegun since I was a pup, without ever thinking about what I was "really" saying.
Riflegun was, and still is to many folks, the same as long gun.
If it ain't a short pistol, then it's got to be a long gun.
Just as, if ain't a short pistol it must be a riflegun....does that make sense to anyone but me?
Terminology varies greatly from area to area, even today, and God only knows how things like this get started.
If you're in the deserts of the Southwest, even today, and some skinner shows you his rifle, or shotgun, there is a good change he's going to tell you he has a riflegun.
The term use to be very common throughout West Texas and New Mexico, especially New Mexico near the Mogollon and Gila Mountains, plus around the Los Alamos / Taos area.....riflegun is the word most often used to describe any kind of long gun.
Here in the Pacific Northwest, it's seldom if ever that I hear the term.
Perhaps it is in recognition, a kind of respect, for the many fur traders that passed through certain areas those many, many winters ago, or perhaps it's just a way of saying I have read a book or three on the subject, and I'm somewhat aware of the terminology used back in the day.
Heck, I'm not sure anyone can offer any real "reason" for this, but I do know it exists.
Technically, I personally believe Pathfinder is spot on in his description.
Still yet, it is what it is in other places and will likely remain so.
The US Army feels much the same as gunmaker about a gun...it's wheel or track mounted and has absolutely nothing to do with anything shoulder fired.
In fact, in the Army, you better never call your rifle a gun, or you'll end up doing strange things that make no sense whatsoever.
Uncle Russ...