The shield is not a big deal. The stuff is not hard nor IMO is it the result of fighting. i have put 240 grain and 250 grain saboted muzzle loader bullets through both "shields"of several boars that weighed over 300 pounds.
This hog was hit with a 250 grain SST bullet from my .50 muzzleloader. Striking velocity was around 1,700 fps. That hog measured over 19 inches through the shoulders. The bullet went through both shields and was under the skin on the far side. The hog was field dressed and skinned. The coyotes ate the 1 1/4" inch thick shields.
A good discussion of the shield: