[quote=LeeRoy]
Addressed to ASTA about his T-51b power armor.
[/quote]

It's actually low tier. It's rated to absorb 2,500 joules of energy, which means it can take bullets ranging between the .44 magnum and the .45-70 Government. Shoot the T-51b with a .50 BMG and the round will pierce the suit, yaw into the target and most likely exit the suit and still retain enough energy to blow a hole through a thin sheet of steel. The ablative surface weathers lasers and radiation emissions, while the helmet's eye port is 'bulletproof' and the power source of the suit has enough fuel to last for 10,000 years. 

To be fair, info on the T-51b is rather vague and subject to a lot of contradictions and 'grey areas', where you're really only left to your own assumptions and predictions regarding the suit's capabilities and performance.