Whats the argument here?
That a .50 cal would be more effective against armored glass than a 20mm?
No. Why? Even the HE rounds are gonna do some damage to the glass, depending on how thick, they might break it or crack it. If it couldn't even damage glass, it would be useless against metal.
And the AP rounds would be better than the .50's at punch through a sheet of glass. Same muzzle velocity + higher mass = more penetration.
And besides, when all it takes is one bullet to hit the pilot, they'd all be about equally effective.
So, should the 410's pilot be so vulnerable? Probably not. It almost certianlly was armored glass, we've seen proof that armored glass can stop 20mm rounds. At ranges above 1000yds, .50's shouldn't be punching through where 20mm's wouldn't.
Is it a bug? Possibly: for a while, the M4(76) had thicker armor on the (left?) hull side than it should have been. We've had bugs before, and we'll have them again in the future.
Is it a decision by HTC? It very well might be exactly that. Who knows what exactly they're trying for. Not us.