One wonders how much melting there is in the sun...
Heh! Yeah. It depends.
It depends on the wax bullet. The orange wax and the red wax are notorious for melting in hot sun. Belle, Zach and I were at a small shoot in Gainesville, TX last year and we were in the very hot north Texas sun. We were shooting the orange wax and had to keep them i the shade, otherwise the bullets would get soft and when struck by the pressure from the primer would deform and come out of the barrel like a big wad of donkey snot. We learned quickly to keep out ammo shaded until just before we went on the line.
I'm tod that Spitfire (red) wax has come out with a high-temp formulation that seems to help They will all melt to some extent, so it's best to keep your ammo shaded. Some folks even bring a small 6-pack cooler to keep their ammo cool, but I'm not sure that's necessary.
Each of those brands of bullets are formulated differently, so they act differently in the barrel and against the target. The blue, and the white are known for being hard and they tend to ricochet off the target. The red and orange are softer and will shatter when they hit the target. The harder bullets are easier to clean up afterwads because they tend to stay together, while the softer ones are harder to clean up because they shatter and leave wax dust everywhere.
I haven't tried the purple wax yet. He's the new kid on the block and I'm still working though stocks I ordered four or five moonths ago.