Sorry for taking this long to chime in guys, but things went dwonhill with my dad. Bloodclots in each lung meant I speant 12 hours on Easter Sunday in the ER.
Anyway, Grant and Gino are spot on!
Space has always been a premium on the Pavehawk, basically since it was never really designed to be a Rescue bird. Any type of weapon system in the rear door area makes my job (operating in and out of the bird) pretty tough to downright impossible. Speed is the key to any CSAR or SOF Infil/Exfil. Not to mention the weight and aforementioned space constraints. She is a powerful bird, fast and built like a brick (rather concrete) Sh@t House but when we load all the necessary mission gear she just doesn't have a lot of room inside. Hell, that's the main reason for the most current Phase III of the Block 152 upgrades...namely the external gun mounts and ammo bins. There are three weapons systems I have seen operationally deployed on the Pavehawk. Namely the M-140, the GAU-2B (USAF for minigun), and the .50 cal. We operated for a little while in Afghanistan with the M-240, but primarily used the GAU-2B in each window. Sometimes you'll see a 50 in one window and a GAU-2B in the other. The 50 is added to give more of a hard target penetration weapon and to add a little more stand off range to supress threats. The problem is that now you have two types of ammo to store, and two very drastically different cyclic rates. What if one runs out before the other? Now you've got one side of the bird undefended. Anyway, you balance all of that with the needs of the mission...environment (high altitude, desert, etc..), customers, objective and you come up with a loadout. Sometimes it becomes an AOR specific thing. Sometimes it's a mission specific thing.
Hope that helps.
Oh yeah...The 50's in the doors was a 442 TES deal out of Nellis, where they evaluated and approved the concept for operations. However, that is the only place that I've ever seen them mounted (for CAPEX's) and I've NEVER seen them like that operationally in the fleet. The 442nd is also the only place you'll see the center nose mounted radar (like the MH-60L), but I'll tell ya this...that's a hell of a lot better place to mount them than they are now...especially here in Alaska. It's pretty easy to ding that thing...and we won't even get into the FLIR location!