Auto-wrap lots of items in Material
You can do that, or you can simply add layout-wrap property to your <div ng-repeat="stat in equipmentStatArray" flex="25"> like this:
<div ng-repeat="stat in equipmentStatArray" flex="25" layout-wrap>
As luck would have it, this is just a flexbox thing. I solved it with some combination of flex-wrap: wrap, display: flex, and setting my own flex attributes (at the time of posting, angular-material had set the flex attributes incorrectly. This has since been corrected).