Some testing we made with the US-S 515P slug (12ga hardened steel slug) loaded in 3" hulls at 1600f/s against ths 50 BMG loaded with both Ball and AP bullets.
Shooting distance: 15m.
Material used: 80mm thick bullet resistant glass.
Upper left: 50 BMG AP. Complete penetration.
Upper Right: 50 BMG Ball. Didn't fully penetrate.
Lower Center: US-S 515P slug. Didn't fully penetrate but went deeper than the 50 BMG Ball.

Lefteris
www.europeancartridgeunlimited.com