The part about the sun warping or "burning out" a barrel is 100% ignorant B.S. As the saying goes, "it's better to be thought of as a fool than to open ones mouth and remove all doubt." Well, this guy opened his mouth. Even if you left a gun out in the heat of the Death Valley sun the barrel would probably never get hotter than about 175-200 degrees, and that's a liberal estimate. 200 degrees is nowhere near the melting point of either high carbon or stainless steel, and is lower than the temperatures the barrel can regularly reach by being fired repeatedly.

The second claim may have some merit. Most powders show some degree of velocity, and therefore pressure, variation with changes in temperature. If a load were worked up to maximum pressure in a given firearm when the temperature is 30 degrees and found to be safe, and then fired in 100 degree weather later on the load could produce dangerously high pressures. However, unlike your self-proclaimed "expert's" claim, it's not the powder that shouldn't have been used in hot weather, but rather the charge weight that was used. If his claim is true, the person who's gun blew up wasn't using the wrong powder necessarily, but rather simply too much of it.

Mike