This misconception keeps going on, an assault rifle is semi auto, 3 shot burst or full auto with a selector switch. You need a Federal weapons permit to own this type of weapon, they don't just give them out. The AR15 "look" rifles sold to the public are semi auto, the same as your friends Ruger, one shot at a time. How many shooters have been NRA members? None.The shooters all do share one trait, mental illness. There are over 300 million guns in the US. If we stopped gun violence in the most gun controlled areas, L.A., Washington DC, New Orleans, New York, Oakland, Detroit, and others we would be near the bottom of the gun violence list worldwide. We should have extremely harsh penalties for gun sales and gun use in the cities I listed. And if we back out suicides it would be even smaller. If someone wants to end their life, they are going to do it, gun, or not.
I don't think there's any misconceptions about semi-auto "assault" style weapons Al, but your point regarding the geography is interesting. A relatively proficient shooter can shoot off a single shot AR15 at a similar rate to a full auto Bren Gun, and there are plenty of examples on YouTube demonstrating this.
Then there's this scary thing, which is totally legal as far as I am aware.
The Bump Stock which rather makes a cock of all the "assault rifle" restrictions such as they are. Someone can always overcome an "engineered" solution and this is clever.
Check this bad boy out..
What is a Bump Stock? Should it be illegal?! - YouTube