Assorted points
The original command "load" meant grasping the barrel of your weapon near the mouth and slamming the butt to the ground whilst groping for a cartridge from your cartridge box, ripping off the bullet from the cartridge and pouring some of the powder onto the frizzen (no spellchecker ??) pan and the rest into the barrel, raising the ramrod from its holder, reversing it and slamming it down the barrel and raise it, spitting the bullet to the hand holding the barrel and then slamming the ramrod again into the barrel to push the bullet as far down as it will go, raising the ramrod, reversing it and putting it back into its holder. You are now "loaded" !!
As for clips, the old Lee-Enfield 303 had clips of 5 rounds which were "loaded"/inserted into the integral magazine.
And, depending on the definition of an "assault rifle", there is that Czech invention, the Brno-Enfield 303 light machine gun, more popularly known as the Bren. It was man portable and had an excellent range and accuracy and pre-dated the German "assault rifle" !!
With regard to the Vietnam War, the M16 was not the only weapon that was highly unpopular with the US troops. An even more unpopular weapon was the "Pig" - the M60 heavy machine gun. It was know to fly apart under heavy use, which rather defeats the purpose of its use !!