The power of a primer is negligible compared to the impact energy of the bullet you press it into, so that's nothing but maybe a spark maker. "Devastator", my ass!
The drill rod section in a shotgun slug would work very well indeed, especially if it was a solid CARBIDE bit and you'd first pointed the penetrator end, which you can do by chucking the bit stub into a drill and then grinding the bit at an angle (maybe 60 degree point) against a grinder with a green wheel. But if the penetrator upsets during firing (contacting the bore surface), it's going to totally wreck the barrel and may even exit through the side of the barrel. Carbide penetrators are especially bad in this respect.
And rather than stick the penetrator in a rifled slug, make a sabot out of a piece of nylon, or better yet, several pieces of nylon, making a discarding sabot. The sabot should lock to the penetrator's shape but should separate easily in the airstream.
A solid carbide, optimally pointed piece of half inch drill rod shaft, weighing what a heavy magnum shot charge does and moving at magnum velocity, should be able to penetrate a good inch or two of steel if not more. It's more than a match for any man worn armor you'll ever see.
CJ