I'm not your little enemy's friend. But you sir are clueless. A 120mm APFSDS round is NOT shoulder fired. It would probably destroy the ambitious guardian trying to do so. It's a tank round sir. A antitank missile / recoilless rifle is a HEAT round. It will explode and in so doing blast through armour by the nature of the size of its explosive payload. It does not 'penetrate' through to hit something 10 feet behind. Since we're talking about realism here, I thought you ought to know. Instead of misleading the kids. Go google those terms or look them up on wiki if you please.

Again, there are 30mm DU rounds that melt through armor, if 20mm rounds can be fired with a shoulder mounted rifle as has been done, a 30mm could as well, would just need to be huge. And also, many of these walls are just standard building materials, they had AP rounds in the 30's that would go through steel plate. Modern .50bmg AP tungsten core rounds fired from a Barrett shoulder fired semi auto tactical rifle will go through inches of steel. So why then, given these FACTS, is AP rounds fired from shoulder mounted rifles in a game about the FAR future filled with alien tech that is much more far-fetched a problem?

DU is a direct impact/kinetic energy projectile...it doesn't "melt" through armor. It uses it's mass/velocity to punch through. It's not a magic bullet and has obvious limitations. HEAT/EFP technology uses shaped charge/super heated molten metal to destroy armor. There is a lot of wiki/Internet expertise bring spouted in here. Listen to military folks concerning munitions and their application.