In a stressed society with low friction access to fierams, buying an assault rifle is just working your way towards Nash equilibrium. Terrifying.
Do you mean an actual assault rifle, or just a "scary black gun" that is functionally equivalent to any other modern semi-automatic hunting rifle (and shoots lower powered rounds than many common hunting rifles)? If it's the former, there's nothing low-friction about it. You have to fill out more forms, pay more money, get more background checks, etc. etc., yadda yadda, and you can't buy any such weapon manufactured…
My experience of firearms is limited to three years in the (not US) military so I'll deffer to you on comparative merits of semi automatic vs hunting rifles available to civilians on the US market.