Let's start with one of the neatest articles, ever: Why the Taliban Can't Shoot Straight.
http://atwar.blogs.nytimes.com/2010/04/02/the-weakness-of-taliban-marksmanship/If you want to scroll down to the automatic fire section, you can, and it's the key element, but read the rest of it as well... amazingly informative.
From there, you need to figure out the flavor of your game. Are your gangers akin to those of, say, Escape from New York, powerful, in control, and paramilitary-trained with weapons fire? Do you want Batman level Gangers, scary, but beatable by a trained professional, often well-armed, but not the greatest of shots? Do you want realistic gangers which are mostly underfed and undereducated tenagers who talk tough but actually aren't much in a firefight, mostly interested in making a lot of noise and getting home in one piece? (Most of the Taliban guys in the link fall into this area.)
From there, that'll tell you what kinds of weapons you'll see and how they're used.
Pros wil use good gear ... maybe not the TOP of the line, but good, and will know how to fire short bursts and cover one another. Automatics 3 (or 4 if you really feel fancy!), Longarms 2, Pistols 2 (3 for maybe a few), Close Combat 2, and Intimidate 3.
Batman gangers are decently armed, but aren't well-trained in it. They normally burst but some spray-n-pray will be around... most will be using pistols instead of longarms, however, as they're vastly more afforable and concealable. They're not well-trained in them, mainly using them to scare people, but can hit every now and then. They're actually more dangerous in melee. Call it Automatics 1, Pistols 2, Close Combat 2, maaaybe 3, and Intimidate 3.
Real gangers are *terrible* shots, not all that goo din a brawl (But still melee better than they shoot!) and act tougher than they really are. No Automatics skill (Spray n pray all the way!), Pistols 1, Blades 1, Clubs 2, Unarmed 2, Intimidate 2
That'll give you some nice elementas to work with. Again, read that Taliban bit for things about target practice (Nearly nonexistant), amo issues, the effects of poor health on one's ability to fight, education levels, expctations ... amazing stuff.