You should have this discussion with Robert Trifiletti, former Chief of the Army’s Light Armament Division at Picatinny Arsenal.
"Part of the memorandum received from the Army’s Trifiletti stated: “SUBJECT: Freedom of Information Jay H. Greenblatt & Associates “Assault Rifle”.
1. This office researched the definition of the term “assault rifle” by identifying and locating official Department of Defense (DOD) and Department of Army (DA) publications on ordinance technical terminology, DOD/DA technical small arms publications or definitions of military terms.
2. The definition of an “assault rifle” is “Assault rifles are short, compact, select-fire (i.e. both semiautomatic and full-automatic) weapons that fire a cartridge intermediate in power between submachinegun and rifle cartridges.
Since 1944, military firearms that fit this general description and general design have sometimes been labeled as an “assault rifle. Some civilian versions of military look-alike rifle have been erroneously labeled as “assault rifles” because they generally fit the description, however, s ince the civilian rifles have been modified internally to eliminate the selective fire capability, they are not “assault rifles”.
http://www.tulprpc.org/attachments/File/Army_Gives_Definition_Of_Assault_Rifle.pdf