There's a lot of misinformation out there. Just proves that neither side really gives a rip about 20 dead kids. They only care about their agenda.
As I understand it, and there's not much that disputes it, 4 guns were seized. 2 handguns, an AW with a 30 round clip(not 100 rounds) and a shotgun. No one seems to dispute that both handguns were found inside the school. The question seems to be whether the AW or shotgun was found in the car and therefore not used in the massacre.
If the initial reports of several children with "numerous" wounds were correct, I'd probably lean towards the shotgun being used since it was a 30 round clip because he'd have had to have numerous clips. I haven't seen anything listing the number of clips found.