I'm pretty sure I never ran into any gangs with M4s.
Tips that I can think of:
-The M4 is better, the shots don't spread as much from sustaned firing. I'd reccomend having the M4, MP5, and the minigun (it's pretty easy to mow down a whole wave if they come in all close together). Also, make sure you have the sniper rifle, because;
-Sometimes gang members will start running away and you'll have to chase after them so you can finish the wave.
-The best tool for starting gang wars is the SPAS-12 combat shotgun. Walk right up to a group of 4 and blow them away before they get a chance to shoot back.
-BTW, gang wars start once you kill 4 gang members in quick succession. It doesn't matter what gang they are. If you kill 4 Vagos on Ballas turf, it still starts a war with the Ballas. It probably doesn't work if you kill 4 of your own gang on enemy turf, but I haven't checked.
-Also, it doesn't matter where they are. The war starts where you're standing. If you're having trouble with starting a war in one area, try to stand on the edge of it and snipe enemies in another area.
-Above all, don't let them get near you. Your main advantage over the defending hordes is
range. If you can, back up while firing.
-The enemys usually spawn on the roads. Try to stay away from the roads and let the enemy come to you.
-The smaller the space between the attackers, the better. Depending on the terrain, you may be able to get them all to come straight at you. If they're coming at you from two sides, you'll probably die.
-Which reminds me, go in on a bike and park it as close as possible to where you plan to fight from. If things get hairy, you may be able to hop on and book it to the other end of the territory to regroup. Furthurmore;
-Running is not an option. If you abandon a territory in mid battle, it'll go all non-coloured and the enemy will stop spawning there. Not entirely, but they'll be rare enough to make it really really annoying to start another war there.
-The light purple and yellow territories are less heavily defended. If your applicable weapon skills aren't already at gangster level, do these first to get them up.
-Between waves you have a chance to run out and collect the weapon and armour powerups that spawn in. They usually show up fairly obvously in the middle of the road somewhere in the territory you're attacking. Get 'em if you need 'em, save them for later if you don't.
****Don't forget about the Ballas turf in north San Fiero, and the Vagos turf in the town north of the Garver (?) bridge (they're very lightly shaded, look close). It's a total pain in the ass to get these, because gang members hardly ever spawn there, be persistant. Once you start the gang war though, it's only one light wave and the place is yours.
*****You have done all the story missions, right? A bunch of missions before the last one involve taking over turf. If you've already got it, you'll just have to do it again for the mission, so it's kind of a waste of time.
That's all I can think of right now. Hopefully there was something in there you didn't already know
