Stagnation temp at Mach 3.6 at sea level is ballpark 1100F. That is a constant, so bullet temp is
increasing, while the heat source (friction) is removed at barrel exit. Both are probably factors, but the
continuing 1100F applied temp has to be a factor. Exposure is short. A 100 yd shot at 3900 fps,
is 0.077 seconds to the target. Mine were blowing at perhaps 1/2 to 2/3 of that, say 0.05 sec, or
50 milliseconds. Very high conductivity between the hot air and the skin, extremely
high convection coefficient, at that speed.
I remember asking my father how fast his F-4 Phantom II could go. He said, "Mach 2.2" at altitude.
I asked about down low, and he said a lot slower. I asked why, and he explained that the aerodynamic
heating would weaken the wings at over about Mach 1.5-1.7 at low altitudes. Stagnation is in the
~300F range there, enough to start to make aluminum structures.....questionable. My first introduction
to aerodynamic heating at about age 12 or 14.
Bill