Cartridges

[CINDERS]

So I finally found out what the bullet is called with the slits in the side;

Although the Tweedie bullet had the new metal jacket, this covering had slits in the side and a shortened tip exposing the lead core. The result of this arrangement was that, upon striking flesh, the metal jacket mushroomed, or opened up like a flower, increasing the bullet's diameter and resulting in a wide wound channel and a gaping hole if it passed through. Should the bullet be retained in the body, its victim suffered the full effect of its kinetic energy.

As we surmised it was to aid in the expansion and creation of a big wound channel along with shedding its kinetic energy into the target fast.