Like Flags and RR posted, the Partitions are designed for the front half of the bullet to open up and fragment through the first section of the wound channel.
For about 20 years my favorite elk bullet for my .30 Gibbs was the 180 grain Partition. Often I would find the expanded back half of the bullet just under the hide on the off side of the elk. All of the lead in the front half of the bullets had fragmented inside the animals.