Please choose a phrase that still captures the fact that they are designed for killing groups of people in short periods of time.

There's no answer to this question because it's a CNN propaganda line. Please cite literally any genuine source from a weapons designer which explicitly says that semi-automatic rifles are "designed for killing groups of people in short periods of time".

Either you ban semi-automatic firearms (rifles and pistols), or you won't accomplish anything. There's no way to distinguish intent through design. Intent is in the shooter, not the firearm. This is why Feinstein's "assault weapon" ban on pistol grips achieved absolutely nothing. People still buy AR-15s in California every day.