Lead is a relatively soft metal, and the fact that it deforms on impact is what makes lead bullets so deadly. It expands inside whatever it hits causing more damage to the surrounding area. But there are metals much softer than lead, and their effects on contact are even more pronounced—so naturally someone made them into bullets.
In a previous video, The Backyard Scientist filled some shells with sodium and potassium and tested them by shooting the bullets into a fish tank. In that experiment, the softer metals expanded and deformed much faster than lead, blooming into a sort of underwater mushroom-shaped blast. But because their kinetic energy was expended almost immediately the penetrating power was considerably less intense than with traditional bullets.
Thankfully, we aren’t going to find out what that reaction looks like inside a person. But using a watermelon as an analogue, a softer target explodes immediately. And it’s goddamn terrifying! Don’t be deceived by the pyrotechnics. Consider that lead bullets snap right through a cinder block with ease, while the softer metals hardly made a dent.
The sodium doesn’t react with all that water inside the melon. Luckily, a couple aerosol cans are thrown in to feed your hunger for explosions.