Military-style weapons, like AR-15s, AKs, FALs, etc. are far more effective for one person against large groups than anything else and the government seems to have come to believe that American citizens should not be trusted with that kind of ability.
If we had militias in the original sense of militias being groups of armed citizens organized and trained ("regulated") together for the common defense, these would be the appropriate weapons they'd need.
We have since "evolved" to having highly militarized government and police organizations which want themselves to be armed to the teeth and swathed in body armor but want the common citizens to be as unarmed as possible. Anybody see a pattern?
The rush to buy "Assault Weapons" and ammunition is the recognition that a right, a connection to history, a status within our own society is about to be permanently taken away and some of us are scrambling to cling to the last vestige of what we used to be.