What a weird story. So much to unpack here.
400 rounds is nothing to own. Hell, I probably got 2,500+ rounds and shells of assorted crap. I blow through 200 rifle rounds farting around on a Saturday afternoon by myself. But carrying that much 7.62?! Holy shit those look heavy! Loose or in mags, that's a lot to pack around. (I'm only familiar with the typically smaller AR-15 rounds.)
And he was acting an ass like that? If he was there to kill people, he would have. Smells like suicide by cop. Mentally ill for certain. I loathe squad cars being rolled on mental health emergencies, but this was not one of those times.
The cops only fired 7 rounds?! Fear might drive that many trigger pulls out of me alone, let alone combined with a partner. Finally, some cops with professional restraint. They rolled up, just two of them, and handled a seriously dangerous situation with the rock-bottom minimum of violence. This is worthy of applause.
And no, they won't find a larger motive. He was simply nuts. They'll find some crazy, conservative social media, but that's about it.