No, because shotgun slugs (or even buckshot) are so much heavier than a .556 bullet. The tiny .556 bullet tends to tumble when encountering light barriers like drywall and wood. Large, heavy slugs, even if they tumble, have a shape and mass that continues in the same direction. Look at the shape of bullets designed for elephant hunting - they are very similar in shape to shotgun slugs, and are designed to penetrate very thick (many cm) of bone to reach the brain, in a straight line.