look anon, it doesnt matter how much lighter than gun is, youre not using it as your machine gun for dismounted troops. the ammo is simply too heavy. it would still be cool for support and anti-materiel purposes, but its not going to be suppressing the enemy for longer than 2 minutes before you run out of ammo. so for all intents and purposes its mainly going to be a vehicle mounted weapon, or emplaced in a fixed location where the extra weight doesnt really matter. much more important to reduce the weight of something like the m240, imo, since that means less broken backs / more ammo for the infantrymen carrying it.
Japan