If you are a person of law abiding sanity and not a gun owner nor worried about your government - then you are part of my problem. You will likely say, what does anyone need such a firearm for and so many rounds of ammunition? Looking at the civilian population that you think you represent. But the question should be asked of your armed forces - which includes the police and regulatory enforcers.
But you don't ask, although the 2nd Amendment is all about all of us, you won't ask.
So why do the armed forces, the police, the regulatory enforcers need all those weapons and ammunition? Well, to do their job poorly. Ruby Ridge, Waco, Texas, are just two examples and this fine group of excesses done in the name of the government gone so wrong. But then you could have looked at what happens when a community of law enforcement officers think they are being hunted by one of their own-rejected. Don't deliver newspapers in the early morning, ladies.