This homemade, carbide core .50 caliber shotgun slug looks pretty mean, but how does it perform?
As it turns out, not particularly well. However, TAOFLEDERMAUS gives a pretty good analysis of what went wrong during testing. This design features a carbide slug inside of a plastic carrier. The carrier then rests inside of a sabot to ensure a proper gas seal in a 12 gauge barrel ( 0.72 caliber).
The forces from rapidly accelerating the slug caused the heavier carbide core to be pulled through the back. That caused the “armor piercing” core to tumble and ultimately fail.