I actually disagree about hiding in a bush or doing an ambush with the machine guns. If your going to surprise someone, you do it by popping out and putting a few bullets in them real quick, you don't need the machine gun whose only advantage is the ability to pump out a huge number of bullets. If I'm planning on camping in a bush or behind a wall, I use the M14 as Terrorist or the M4A1 (sd) as Seal.
When I'm ready to rush the hell out of some team, thats when I pull out the machine guns. I mainly use them on Terrorist but sometimes Seals too. (like on Frostfire as Seal I use M63 always) Anyway, I use the M60 and the M63 every single day. Most people think they really suck, but they don't, once you get good. In my opinion it's the only terrorist gun that can stand up to an IW or an M4A1. I get 4 kills in a round on a regular basis.
Anyway what I basically do is CHARGE the enemy. With this gun, you aren't trying to use stealth. You want to put yourself in the middle of the most amount of enemies possible. Then start firing and moving in all crazy directions while keeping your crosshairs on head level. Besides you going nuts and shooting all over the place, they will panic and start shooting you and each other as well. If you have a clear bodyshot, go for it and pump a bunch of bullets in, but if theres several guys and you only have several seconds before you know you will die, aim at their heads and hold that trigger down. Keep that trigger held down and just cause as much chaos as possible while blasting those guys. The best is when you come up on the flank of a group of 2-3 guys looking the other direction, and you line it up with their heads and mow them all down. With other guns, you'd run out of bullets and they'd have a chance to counter attack.
Honestly, I think people get scared by a guy who knows what he's doing coming at them with the machine gun. It just sounds deadly.. and can be one of the deadliest guns in the game... Keep moving and firing as you move deeper into their territory. If you know theres a guy behind a wall, just unload at him before you even get there, so when he pops out, he does so into a spray of bullets. Dont camp... keep moving so you can get to that next guy or group of guys and cause some chaos. Even if you don't get a lot of kills, you can definately cause a huge distraction and help your team get kills.. plus I'm telling you that people WILL KILL their teammates FOR YOU when they panic at you shooting all over the place.
I will also say that the machine guns have very little recoil but at the same time, they spray bullets all over the place and it's not the most accurate gun. However the lack of recoil really allows you to keep the gun generally on head level and get those headshots. You can read more about how I get headshots in my FAQ.. and also my HK5K Method thread, if you haven't read it already:
http://www.socom3.com/phpBB2/viewtop...ht=hk5k+method
Due to the lack of recoil, the same method I present with the HKs works with the M60s. Hope this helps.