cooked it! What did I do wrong?

Your piston looks quite reminiscent of a piston I fried in a supercharged engine I have. (Albeit not a mopar)
The engine was always very relaible, and took the beatings I used to give it like a trooper. It finally did what you see in the picture, after a prolonged high speed pull into a strong head wind on a hot day. My theory is that the charger heat soaked and lead to detonation that I couldn't hear till after the damage was done.