1) The AWB didn't ban assault rifles, those were already restricted 30 years prior in the 1968 Gun Control Act. They banned scary looking rifles like banning spoilers to prevent speeding. By the way 2% of all homicides and 1% of violent crime involve a rifle of any kind. "Scary black rifles" are a tiny fraction of that already tiny percentage. The Clinton DOJ concluded their is no evidence the AWB did ANYTHING to reduce crime or homicides.
2) The founders saw no issue with citizens owning "military weapons". This was the "assault rifle" of its day.
http://en.wikipedia.org/wiki/Kentucky_rifleThe Kentucky Long Rile a uniquely American design. The longer rifle allowed for amazing accuracy in the hands of a skilled user (and the American colonists needing to rely on it for protection, and food were very killed). The long barrel also allowed for higher velocity. Blackpowder burs much slower than modern smokeless powder. The long barrel allowed time for more of the powder to burn.
Against tightly packed British formation it truly was an "assault weapon". The high velocity and accuracy allowed Minutemen to fire a half inch lead ball with deadly results. The incredible muzzle velocity compared to comparable weapons allowed it to go straight through two or three ranks of men resulting in multiple casualties per shot.
As the war progressed the skill, accuracy, and lethality of the American rifleman became known world over even forcing the superpower of its day (British Empire) to change tactics against this new threat.