Lead is a relatively soft metal, and the fact that it deforms 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 than 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! Lead bullets were also able to snap right through a cinder block with ease but the soft metals hardly made a dent.
Strangely the sodium doesn't really react with all that water inside the melon. But don't worry, a couple aerosol cans are thrown in for good measure to feed your hunger for explosions.