OK... I am not an expert, don't claim to be one, and don't play one on TV. But I did some research, and found this in "Swords and Blades of the American Revolution" by George C. Neumann (who *is* an expert). Neumann had this to say about Rifleman's knives (calling them Belt Knives in his book):
"Just as the colonists evolved the European 'Jaeger' rifle into the Pennsylvania long rifle to meet the needs of the New World, so the sophisticated and specialized blades of Europe gave way in America to simple all purpose knives which could whittle, carve, skin, chop, stab, and scalp.
"The longer sizes are generally thought of as 'rifleman's knives'-since with the rifle and tomahawk they constituted the frontiersman's basic equipment. The blade often reached 12 or more inches, and could include a false edge (but seldom the sharpened clipped point of the later Bowie patterns). It was essentially a butcher's knife---having it's single edge and 'choil' create an off center appearance to the blade. The simple guard and hilt mountings are usually iron, brass, pewter, or silver, and the individualized grips were generally of wood (eg. hickory, maple, walnut, apple, cherry), horn, bone, or antler. The majority of blades were imported, but many were created by local blacksmiths, or fashioned from old file, saws, or swords. During the 1700s, they were commonly referred to as 'butcher' or 'scalping' knives. (Note: there was no recognized 'scalping' pattern; each colonist or Indian apparently used his regular knife for that purpose).
"Smaller versions of this belt type with blades of 5 to 6 inches were also popular, as evidenced by excavations from camp sites."
"Swords and Blades.." also illustrates photographs of 23+ "Belt Knives," with blade lengths ranging from 5" to 11 5/8", with most being in the 7" to 9" range.
FWIW --JB