The gun control movement has wasted its energy on the "assault weapon" for twenty years, and you have nothing to show for it. You can not - short of a 2nd amendment repeal - ban the AR-15. Here's why:
This is a semiautomatic rifle that is not considered an "assault weapon" by NY or California. It is semiautomatic because every time you pull the trigger, one bullet is fired. The gun fires as fast as you can pull the trigger.
These are tacticool add-ons that gun owners who play too much Call of Duty like to buy. In addition to making the weapon look more militaristic, they do have the benefit of making the weapon more ergonomic - more comfortable - to hold. They do not change the rate of fire of the gun.
This is what you get when you combine the rifle and the add-ons posted above. A gun that is somewhat more comfortable to hold, and
exactly as lethal as it was before. It is also now illegal in NY, California, and anywhere else "assault weapons" are banned.
Why? Because "assault weapon" is a misappropriated term. The original assault rifle was invented by the Nazis at the end of WWII. It was a fully automatic weapon - a machine-gun. When you hold down the trigger, the gun would fire and keep firing until you let go or ran out of ammunition. Machine-guns have been illegal for civilian use since 1934. None of the high profile shootings you mentioned involved a machine gun, and machine guns are almost never used in crimes due to the extreme difficulty of obtaining them. The term "assault weapon" came about in the late 20th century as a means to describe semiautomatic rifles that had military style ergonomics. This was done because a ban on assault weapons would appease Bill Clinton's base without infuriating republicans too much. In other words, it was an attempt to look "tough on crime" without making any substantive changes.
The reality is that assault style weapons are exactly as dangerous as any other semiautomatic weapon. In fact, the deadliest mass shooting in America, the Virginia Tech shooting, was perpetrated with handguns. On a mechanical level, all these weapons are functionally the same. If you want to ban semiautomatic guns, you'd be banning such a large percentage of the guns currently in use that it would be a de facto repeal of the 2nd amendment. If you wanted to ban the military ergonomics associated with the AR-15 while leaving the 2nd amendment in place, as New York did, you end up with the reverse of the process displayed above.
Gun owners in New York immediately took this AR-15 and stripped it of the newly banned features.
This was the result. An ugly, uncomfortable, and
equally deadly weapon in full compliance with the strictest assault weapons ban in the nation.
If you want to save lives focus on things that actually make a difference; handguns (their concealability results in them being used in 90% of gun deaths), loopholes (like the one in the OP), and an open, voluntary, no criminal liability gun buyback program.