The Backyard Scientist fired bullets filled with liquid sodium, potassium, and a sodium potassium alloy at watermelons, cans of starter fluid, and other objects with explosive results. I have never heard of such bullets before but results are awesome!
The reactive liquid metals behave differently than a traditional lead bullet. They are much more destructive against soft targets like watermelon, but mostly ineffective against harder materials like the cinder block.
Check out the process of making the bullets and this video is also in glorious slow motion.