If you want to know why anyone would "need" a 30 round magazine, here's one example (out of thousands) from Pensecola, Fla in Sep 2009. This was a jackass who killed two police officers in this area and ultimately was stopped by the police. He took 15 verified rounds according to the autopsy report from police fire before shooting himself in the head, and the police fired many more that missed.
That's right -- after absorbing 15 rounds he still had enough fight left in him to commit suicide.
The real world is not as depicted in the movies.
Then you take the recent event where the lady retreated with her children into the ATTIC when she heard an intruder breaking into her house. When he entered the attic, she shot him SIX times and he still was able to get out of the house to attempt escape.
One shot my wazoo!!