@Paris
Yes, that's with full metal rounds, rather than nuclear, but I'd think that's what you have to worry about. Nuclear rounds, if they're used at a safe distance, are gonna be hard to get a direct hit with. If used at close range, they'll hurt the user too.
Now, if five layers of armor is able to deal with a nuke round going off twenty meters away, and two layers isn't, that's a point against my idea. However, I think the HGC is intended more for use as artillery, for killing groups of civvies, rather than taking out Battlesuits. I wouldn't be surprised if two layers of armor can tank a nearby nuke.
Also, what, AP rounds? The basic round is solid metal. What would an AP round be? Mythril penetrator core? Kinetic amp tip?
@Nik
I think you got confused there. I'm not saying to shove a robot body in there, I'm sayig to only shove the braincase in there, and directly connect it to the battlesuit's stuff, so the battlesuit literally becomes your body. That way, there doesn't need to be room for all those squishy useless things like lungs and legs, and it doesn't need a cockpit with keyboards and everything. Just a connection to your brain.
And I think you underestimate how good our Man-Machine interfaces already are. Jim could play some Mario game entirely inside his head, as well as Flint who had lots of monitors and keyboards. I think Jim might have actually had an advantage. Beyond that, Saint already programs stuff using nothing more than his braincase thoughts- his tablet's basically just extra memory and proccessing power. Lots of people send complex text and voice messages with nothing but a thought. Controlling limbs and a few binary switches shouldn't be difficult.
And yes, it is kind of a larger version of Milno's suit. Primary differences are that it's cheaper, better armored, and uses actual fully steel robotic limbs instead of flesh. Also, instead of operating a bunch of complex functions with your tounge and chin, you can operate them with a mere thought.