In the nutshell and as regarding the Stoner 63 modular weapons system:
1. Ideally suited for special operation type missions of one or two days at the most.
2. Too delicate for prolonged and general type of infantry military duty. Stoner required excessive maintenance and cleaning. Stoner a weapons system seen as too finicky and delicate. Perhaps even as seen as too advanced?
3. Fired the same ammo regardless of weapon. This commonality is an advantage?
Stoner a weapon as could be configured using a variety of barrels, stocks, feed mechanisms.
Configurations to include:
* An assault rifle.
* A heavy-barrel automatic rifle.
* A light "commando" machine gun.
* A medium machine gun.
* A carbine.
* A survival rifle.
Assault rifle as defined possessing a detachable high-capacity magazine, pistol grip stock, selective fire option, semi-automatic or automatic. Modern assault rifles [as would the Stoner] also firing that intermediate [medium] cartridge and round.
That heavy-barrel automatic rifle seen as a valid replacement for the Browning Automatic Rifle [BAR]. A squad level automatic weapon.
All configurations of Stoner firing a common round, again that intermediate cartridge and round. Commonality of ammunition seen as a big plus?