A Tale of Two Threads:
Lubrication:
AR’s need lubrication. Plain and simple. Wet or dry, I don’t care - they need to be lubricated to run properly. When guys are fighting with their rifle, they may not have time nor interest in stopping to check lubrication after a couple mags of fire, so “running wet” up front helps ensure when things get hectic, the rifle doesn’t get too dry as lube thins from heat, flows from movement, fouls from powder or dust.
I’ve been in the “my AR is so wet, it sprays Mobil 1 all over with every shot,” camp, and I’ve used Hornady 1 shot dry lube, as well as frog lube. Many, many things work. If it sounds dry when you manually cycle it, then it IS dry, and you’re risking feed failures.
Temperature and rate of fire:
“Too hot to touch” is an exceptionally popular rule of thumb - or maybe rule of hand - but it’s complete bunk, and has no bearing based in science or metallurgy. The typical threshold for “too hot to touch” is nowhere near hot enough to cause any issues for any barrel steel. 1 second of skin contact with 160 can cause 3rd degree burns. This isn’t an “ouch that’s hot” or “wow, that’s too hot to hold onto” temperature - this is causing a burn entirely through the dermal layer and burning into the fat and muscle beneath. This isn’t a “I touched it and have a red mark” first degree burn or “it blistered my finger” second degree burn temp - this is burning completely through your skin. This is one of those “your hand jerked away and then you found coursing pain through your entire arm, and now need to go to the hospital because the sealed layer protecting your internal organs has been compromised,” type of things. 160 degrees, for less than a second. Steel’s not doing anything at 160, not even thinking about doing anything. Not for twice that, and twice again.
Comparatively, most folks will quickly let go of anything over 120 degrees. This isn’t even yet hot enough to cause 2nd degree, blistering burns after 5+ seconds of contact (threshold typically 140 @ 5 sec), but people will touch and let go of anything over 120, very quickly. A black leather motorcycle seat on a 100 degree, sunny day can exceed 120F, as a point of reference. 120 typically doesn’t cause 2nd degree, blistering burns instantaneously.
The math to determine the internal temperature isn’t so difficult, but you can be sure, the heat transfer to reach only 120F on the outside isn’t very long if your sustained internal bore temp is in excess of 980F (approx first phase shift for stainless).
It’s possible to get a barrel hot enough to cause damage, but “too hot to touch” isn’t a viable measure.