As I wrote in the other thread, I also prefer to distinguish between assault rifles that fire intermediate-power cartridges and battle rifles that use full-power rounds.As far a the classification battle rifle or main battle rifle,I'm not sure when the term was coined,but in my opinion rifles that fire full size cartridges are NOT assault rifles.
I might be misremembering, but I think the "battle rifle" term has been used by civilian authors for little more than two decades. I used to have a special issue magazine that Chuck Taylor put out when he was editor of SWAT in the 1980s, in which he had separate chapters for assault rifles and battle rifles. I don't recall any writers using "battle rifle" back in the 1960s, though, the time period when The World's Assault Rifles was published. And, as I noted, the military didn't use "battle rifle" until this decade.
I have no idea who came up with "main battle rifle," but suspect it was some civilian with no military experience who heard of main battle tanks and decided it'd sound cool to copy the phrase.La France Specialties called their 8" barreled M16K a "high-power submachine gun." The reasoning, as I understand it, that some individuals refer to weapons like the AKSU as SMGs is not solely the size, but primarily because such short-barreled assault rifles are intended for the same missions/roles as true (pistol-caliber) SMGs. For instance, the 5.56mm M16K was marketed as an alternative to the 9mm MP5.Some people consider the AKSU-74 a submachine gun.While clearly it fires an assault rifle cartridge.In my understanding a submachine gun fires pistol caliber catridge.Therefore I don't understand why simply based on size it's classified by some as such.I'm no expert,but it makes no sense to me.