Mercy is for the weak. Here, in the streets, in competition: A man confronts you, he is the enemy. An enemy deserves no mercy.
The Colt M4 Commando. When you absolutely positively must kill every muthafucka in the room... with a headshot... accept no substitutes. 5.56x45mm rounds, 30 round magazine. 11 1/2 inch barrel length, the shortest in the M4 family, almost short enough that you could call it a sub-machine gun, perfect for the urban environment where pieing off around corners with the shortest barrel possible is always an advantage. As far as I know, you can even completely submerge them in dirty water and they'll still fire. Maybe one of these days when I'm not feeling like such a tightwad, I'll drop about $1500 on one with all the mods I've always been dreaming of. I have shot one before, and lemme tell you, if you've ever fired an AR format rifle before, you KNOW why the US military uses these. Very little recoil considering the carbine barrel length, easily modded for any situation and personal taste, positively superb range and accuracy. This is why we always kill a lot more of them than do of us. They aren't cheap at all, but you get every bit of what you pay for. If those little kids popping out of windows in Afghanistan were firing these at our troops instead of shitty east asian made kalashnikovs, there'd be a lot more dead on our side. Like I said though, lucky for us they're kinda expensive and they can't afford them, so while they're blind-firing one handed around corners and shooting up at the sky or directly into the dirt, we're popping heads apart like pimples at a middle school prom.