Ronan, I'am a real soldier... in an Infantry unit.. I kinda know a little what its like to carry a weapon, using a sling, etc.
Also, I was talking about Airsoft not the Military where we have to use our hands to work on equipment, handle detainees, etc, etc. Yes there are times when you need a sling, but for the majority of time in Airsoft(least with my experiance) you don't need a sling.
Ronin you can use a radio with one hand.. if its a FRS or you got a handset/headset for a radio.. also you really shouldn't be eating while on patrol, especially if its something that requires you too use both hands. If you are eating back at your own area, or off the field you can put the weapon down.
also, this guy has no sling on his rifle, least I didn't see one.
http://www.bottomlineradio.net/images/soldier.jpg
For using a sling for shooting, yea if you got time to aim your shoots, get the sling tight, etc yea its good, but again from my experiance you don't have the time, an you want to be flexible, an plus most engagements are at pretty short range so not really a big deal.
Drake, yea thats a good point wasn't thinking about the pistol thing, but I was mostly just focusing on what was being said (SR25 is heavy). I just got the idea of him walking around in the field carrying the rifle slung because the rifle was starting to get too heavy.
One last thing Ronan, don't take a jab at me can call me cheap(dunno if that was meant, but it kinda sounded like it).