a 12 gauge slug is nothing more than pellets. So that is taking something hard (tungsten) and hammering it against the steel plate.
It probably won't go far at all.
Armour piercing rounds are extremely long hard and narrow. Like a long blade. Pellets are blunt.
I don't know... but yeah that sounds right...
However... and I am not a machinist, fabricator, or whatever...
I believe if you can attach a long and narrow hard skinny round to the slug (powder), and fabricate a barrel that has notches on the inside so that it creates very long and twirling recesses in the metal, that will put spin on the round and allow for the bullet exiting the gun to stay stable.
The downside is that you will lose speed due to the holes that will allow pressure to escape...
I don't know if anti-tank rounds are high speed or what, but those panzerchrects they have zero distance to travel when the explosives go off, so there is pressure, but no speed. I am sure it translates to a high speed round though...
Unfortunately I am no engineer... nor do I know anything about guns...
Here's a 12 gauge hallow point...
Personally though, an I am no metalurgist, but that doesn't look like armour... it looks incredibly thin... I mean what 1/8 of an inch, maybe a little more?
Cars aren't even made from metal anymore these days... they are all plastic and carbon fibre... I mean a scratch on a bumper requires that the entire bumper be replaces with a brand new carbon fiber bumper.
It is the engine blocks that are the only real bullet stoppers, no?
I'd guess that if a car's body (frame) is a strong metal, that surely all it's plate is really nothing more than thin aluminum and carbon fibre and plastic and cloth.