The 10 years for the 2004-2014 Assault Weapons Ban was not even a "study". It was the IMPLEMENTATION of an AWB which the authors had been trying to ram through Congress for over two decades after their handgun bans failed to pass.
That means, instead of a statistical sample of various locations and groups, you have THE ENTIRE NATION and EVERY SINGLE GUN OWNER and EVERY SINGLE REAL LIFE CRIME to include in your reports.
The reports are not forecasts, but actual results. This is more concrete and demonstrable than ANY study could ever be. You are evaluating actual results, not a bunch of extrapolations and polling surveys.
To me, you could not ask for a better population of "study" data than this. Arguing these 10 years was insufficient to have any effect is totally ridiculous. It perfectly illustrated this one important fact above all others: in violent crimes involving guns, the type of gun used is incidental. Look at ACTUAL crimes and the ACTUAL guns used. AR-15 style weapons have always been limited to a small percentage of crimes. Even though an event like Sandy Hook may result in 20+ deaths, that represents ONE criminal using ONE AR-15 in ONE event.
Had there been 20+ incidents of 20+ criminals using 20+ AR-15s, maybe then we would see a need for another AWB.