I had been doing some slowfire before hand for groups at 100 yards (which were not as good as usual... but I had just switched to the polymer coated Wolf FMJ. Before, I was using the laquered HP... I don't know if it was that, or the fact that my front swivel stud was torqued in a little more firmly than usual, and locktyted in my effort to get it to stay put).
Anyhow, after the slowfire, I dumped five mags through about as fast as I could pull and change mags.
I did fire more than 150rds that day, but there is no way that the barrel was any hotter than "lukewarm" when I started. I remember checking to make sure I could grab the barrel with no discomfort prior to the 150rds.
At over $50 a pop for new handguards though, I don't know if I'll be inclined to find out if it was a bad peice of plastic or not.
Next range trip, I will have the new handguard and sling on there, and the sling stud will not be as tight as it was last time. If the groups don't go back to the way they were, I won't know whether to chalk it up to the ammo change, or the 150rd speed test...