The guy is nuts if he thinks the barrels are going to be damaged by heat in a guncase from nothing but sunlight-generated heat!

I have never heard of pressures rising so high with a normal load that a gun was burst due to overheating from the sun. However, it COULD JUST BE POSSIBLE WITH A SHOTGUN, with certain powders, if the charge was on or just over the ragged edge to begin with!

I once knew an accident prone turkey who blew up a nice over/under with an excessive reload he had prepared. He was using Red Dot in a progressive reloader, with a charge-bar set up to throw skeet loads. He looked into each case, and noted that some LOOKED LIKE they didn't have enough powder in them!! So, he took a pinch of powder out of the hopper, and sprinkled "a little more" into the "undercharged" hulls. Later on, he also added a few extra pellets of shot to the shot columns before crimping the rounds. We know this, because he told us what he had done after we took apart the remaining shells, and found excessive powder and shot weights in most of them! We knew the loading tool had not dispensed the excessive quantities, because it was working OK when it was checked out!

It's a good thing he was using a gun with a heavy/massive breech section. This is all that prevented him from losing his head. A 3" jagged piece of the blown barrel went through his forearm, then THROUGH THE HOOD OF HIS CAR, which he was standing beside when the gun went! A friend took him to the hospital, where he was prevented from bleeding to death.