In the 25 mass murders since 2004 (which actually started in 2005) I can only find reference to four shootings that used an AWB banned weapon. Two AKs and two ARs, a couple tactical shotguns, all the rest were carried out with pistols. Although some (a few) of the pistols had high or very high capacity magazines.
I don't know what kind of point I'm trying to make, but it would seem that "Assault Weapons" are rarely used and account for less than 1 in 5 mass murders or spree shootings.
Less than 2% of all homicides/suicides occure with a weapon that was listed on the AWB.
There were other findings of "Assault Weapons" used to commit murder but they were single accounts or same weapon used over time (D.C. sniper) where they were probably just a poor choice and any rifle would do.
I suppose it doesn't matter much, the pantywaists in congress are going to go after black guns and magazines over 10-rds and they will soon become collectors items and rarely seen outside a Three Gun Competition Match.
Sad, how far we have fallen...