If you are doing full-auto firing, there will be a limited amount of mag dumps you could do before cook-offs start happening.

In a 75 degree room temperature environment, you might get about 6 mags dumped consecutively, before you start cooking off.
In a 150 degree environment, meaning it's 120 and the gun has been sitting in the sun, you might only get half that number of mags dumped consecutively berfore cook-offs start happening.
Naturally, this can vary somewhat, depending on the exact conditions involved, and how fast the rate of fire of the gun is, and stuff like that.
By "consecutively" I mean as fast as you can change mags and continue firing.

If I were going over there and there was some heavy full-auto firing going on, during a hot afternoon in the sandbox, I'd make damn sure that I didn't get any muzzles waved in my direction after firing ceased. You could go thru 3 mag dumps real quick, and so could your buddies. After that, all your weapons could potentially be hot enough to cook-off a round left in the chamber, and sometimes it might take 20 or 30 seconds before it happens. Having the safety on is no help in this situation, if there is a round in a hot chamber, and it can cook off. Be very careful with your muzzle discipline, and watch everybody else's muzzle discipline too.
Locking the bolt back after you're done firing will ensure that the chamber is empty, and also allows better cooling of the barrel.

If you fire only semi-auto, it should be a bit better, but it still could happen at some point.

Regarding the mechanical things that might happen, the barrel will get hot, and IF there are any bad stress risers that occurred during manufacture, the point of aim could wander some as it gets hot. With the short barrel and short ranges for firing, this might be less problematic than a longer barrel and longer ranges for firing.

With an 11.5", the rate of fire is fairly quick, and with alot of extended firing, the gas port could/will erode wider open, and this will cause the rate of fire to increase. If it increases over 1000rpm, it could be too fast for some magazine springs to keep up with the cyclic speed. If you notice your gun going over 1000rpm, it might be advisable to change to a heavier buffer at that time.

Wear good gloves. Everything gets really hot over there, even if you're not firing. Many things get too hot to even touch, just laying in the sun.