I was going to speculate that the bullet started out with an internal air pocket but other members beat me to it. I'll refine that speculation by adding the air pocket was so close to the rear edge and side of the bullet that it took less pressure to collapse the side of the bullet then it would have taken to move the bullet forward. The gas had to get out some how. These bullets are swaged out of soft lead wire. The volume of the void probably should have held ~ 59 grains of lead.

If there is a hole in the collapsed side of the bullet then maybe the nose started out partially hollow so the gas could blow it forward by that would not explain how the nose became a long point. As pointed out above gas blow by does not melt lead. The time the lead is exposed to hot gas is too short. Various shotgun, space filler and muzzle loader wads are not singed by the hot gas. A normal .357 Magnum charge will not even change the surface texture of Styrofoam egg carton material when it is used as a substitute for a gas check.

While I can not explain the sharp pointy nose I can also add some thing that has no bearing on this case. When soft swaged hollow base wadcutters are way over charged only the bullet noses leave the gun as a round disks. The skirts freeze the case walls against the chamber walls. The rear of the cases move back independently severing them from forward portion of the cases. Someone had to run the experiment, right? If you must do this stuff I recommend using a .357 with a huge cylinder.