Creative Speculation

.....at zero degrees Celsius, I can drip molten candle wax onto an ice cube and the ice cube will retain its shape pretty well and the wax will harden. As the temperature rises above zero, my ice cube disappears but the wax will retain its form. I would say the concrete heated somewhere else, cooled on the guns which were later themselves exposed to very high heat. The concrete has excreted its 'meltable' parts such as sand and really can't change its form anymore (think of oxidizing your cheese melt) so it retains the form of the guns.

Still, I wish we could get someone to test these objects.