The pins are cut and have sharp edges and burs on their tips, tumble the media for several hours to wear down the sharp ends.
If you go to the STM website
Brass Cleaning & Reloading Tips and Instructions it tells you the following.
"Notice. It takes a few times to get the media broke in"
Below is what happens when you do not break the pins in, the sharp ends of the pins will scratch and gouge the hell out of your brass. When all else fails read the directions (RTFM)