There are other considerations we should consider. The AS is not likely to be well-trained. He will probably experience tunnel-vision and may have a weapon malfunction, as in Aurora. He is also not expecting a fight, which is why he chose a soft-target. All of these things work to our advantage, even if his has a more powerful weapon than we do.
See the Jeanne Assam interview here: http://www.youtube.com/watch?v=2sGx_acSmzw
There are things in our favor, even is the situation is far from optimum.