I think you point the gun at them and tell them to surrender, and if for some reason they're insane enough not to comply you pull the trigger and hope for the best.
In that case why don't spree killers use shotguns? Seeing as they're supposedly more effective.
I don't know where that Canada stat comes from, I've heard it myself but I don't think it's correct.
http://en.wikipedia.org/wiki/Number_...ita_by_country
Canada has less than 1/3rd the number of guns per capita, America has almost as many guns as people and is a massive outlier. I wonder if that statistic was originally "registered gun owners" or something.