This is the lead of the 3-piece bullet. So the idea is to correct the bullet's path and to have extra force after first impact. So as mentioned bullet is made of 3 parts. 1. Slug - which fires out of a special gun and contains some gun powder and spiral spring to spin the bullet. 2. Middle part which spins the bullet (beside the gun barrel's effect) and this part contains also a portion of gun powder so and attached 3rd part of the bullet. So when the bullet hits it's first target the gunpowder ignites and releases the 3rd part of the bullet which continues it's original path even after first impact. So on the image you can see the 3rd part. The main lead which goes further even after impact. And those 2 spiral tails help it to spin and therefore to maintain it's dynamics.
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