I'm destroying the assault rifle type and concept.
The assault rifle came from Germany's Hitler and his designating the Stg. 44 automatic rifle "Sturmgewehr," or "storm rifle," as in storming your enemies with a quick to fire, handy, light rifle. The moniker was created as propaganda. The storm rifle concept translates to the assault rifle. Once it was demonstrated, the USA and Russia had to develop their own, due to the wide variety of tactics such a rifle concept brings.
But it gets muddy. Where the Germans were ingenious in shortening the full power 8mm Mauser cartridge to be in line with distances that a storm rifle would be best at and the Russians did something of the same, the US still held onto bigger is better and range is good. One thing that's worth giving credit is shortening the .30-06 cartridge from 63 millimeters to 51, it made it more efficient and effective for automatic fire, and in some cases, lightened overall weight. It would take until the '60s that a light rifle round was developed, and even then, it was far smaller than the German 8mm and the Russian 7.62x39. The .223 Remington/5.56x45 NATO dumps the "intermediate cartridge" right on it's head.
What it does do is create the concept that fire from a small, lightweight, light recoil rifle cartridge would reduce soldier carry weight (and allow carrying more versus full power rifle) and produce more accurate volley of rifle fire, where it was easier to maintain target sight picture.
The M-16 has been sometimes thought of as a rifleman's assault rifle, (oops I said it) and the AK-47 a submachine of an assault rifle. With that in mind, there's two different tactics applied to each while in the same rifle type.
But back in the '50s, the US was extremely pushy about the adoption of the 7.62 NATO, so everyone making an automatic rifle had to use it. So you had the FN FAL, M14 and the H&K G3, and before that, the Spanish CETME which would license out to make the G3. All in 7.62.
These rifles were rather terrible on full auto, plus big and very heavy. But they have advantages.
Though the small caliber race (US 5.56 and USSR 5.45) brought low recoil, easier sight picture, more accurate automatic fire, 7.62 has reach and barrier destruction. Barrier destruction for sure, the light calibers cannot compete with.
The term "assault rifle" lightly touches all automatic rifle types, but certain calibers, features and characteristics allow some to work in other usage and tactics. For example, the FN (Fabrique National) SCAR comes in Light (SCAR-L) and Heavy (SCAR-H). Light in 5.56, Heavy in 7.62. Both are built nearly identical. This is a simple designation of type. I think it could work for many others. You can have a light automatic rifle, and a heavy automatic rifle.
A really great example of what conceptually was thought not to work coming out of the '60s that may work today is the usage of 7.62 automatic rifles. Rifles of that type in the '50s and '60s were heavy and long, and highly promoted for automatic fire. Today, in Turkey, their new military rifle is a lightweight, ready for modern optics automatic rifle in 7.62 NATO, where the emphasis is .30 Cal gives a bit more reach, barrier destruction, semi-auto fire as normal usage, automatic fire as "Use in case of emergency." Firing on automatic fire has it's place in short range instead of long range. It's a tool. The idea is not to deprive the user of something because historically it was inaccurate at long range and uncomfortable. It is a tool to be used in efficient and appropriate situations.
