after rereading some of the basic rules, i've come across some more rules, we played out wrong it seems. pierce always bugged us to some extend. we play it that way:
monster attacks with 10 damage, pierce 3 against 5 armor -> 5 damage go over the 5 armor and 3 pierce through, 8 wounds total.
monster attacks with 5 damage, pierce 3 against 5 armor -> 0 damage go over the 5 armor and 3 pierce through, 3 wounds total.
now the shield reads it cannot block damage that ignores armor, so we though it couldn't block pierce damage, but after reading through pierce again, i've come across that last part that says, that shields ignore pierce, which means you actually can use a shield to reduce piercing damage, right?
skull shield gives you +5 armor against breath. does that mean, that +5 armor cannot be pierced by a breathing hell hound either, but wouldn't apply to a normal attack from a hell hound at all, in which case you could only reduce the wounds by two by using the shield itself?