http://www.europeancartridgeunlimited.com/en/usslug.html

The US-S (Ultra Solid-Smoothbore) slug as its name implies is a solid slug that offers deepest penetration possible from a smoothbore shotgun barrel.
The US-S slug has a .629 diameter, is machined from brass bar stock and is of the flat nose design with a meplat diameter of .510.
The US-S slug is encased in a sabot and there is also a stabilizing wad that is mechanically locked at the base of the slug by a protruding stud making it a one piece slug ready to be loaded in a primed and powdered hull.
Immediately after firing, the four petals that comprise the sabot break away due to air resistance, leaving the US-S slug and its attached stabilizing base to continue their travel to the target.

The US-S slug is machined in cnc horizontal machining centers with plus or minus .0002 tolerances to all its dimensions. The specific brass alloy used has a hardness of 120 Brinell.
That, along with the flat nose, undeforming design, gives the US-S slug straight unyielding penetration to any game animal used.
As of now, the US-S slug is available in 12 gauge with three different lengths (weights) for the three different hull lengths that 12 gauge shotguns are chambered.

US-S 570 for 2-3/4” chambers. Total slug weight is 570 grain.
US-S 700 for 3” chambers. Total slug weight is 700 grain.

US-S 970 for 3-1/2” chambers. Total slug weight is 970 grain.

Expected muzzle velocities are 1500 to 1600f/s for the US-S 570, 1400 to 1500f/s for the US-S 700 and 1200 to 1300f/s for the US-S 970, all under standard pressures.
The US-S slug must not be used in overbored shotgun barrels having a bore diameter bigger than .732. Also, best choke constriction is cylinder or improved cylinder and for safety reasons it must never be used in chokes tighter than modified.
The US-S slug is the first premium slug available for 12 gauge smoothbore shotguns and although designed as such it could be used equally well in fully rifled shotgun barrels or smoothbore barrels equipped with an appropriate rifled choke tube.
The US-S slug is offered by European Cartridge Unlimited as a component only, in packages of 25 slugs, to be loaded by handloaders and shotshell manufacturers..

the US-S 515P slug, machined of steel and hardened at 60 Rockwell "C".

penetration on steel looks very good, its not flesh and bone but worth a try I would say