REGARDLESS of caliber. 308, 3006, 8x57 Mauser, 7.7Jap all had MANY failurse to stop men with chest hits. It's just going to happen, about 10% of the time, with ball ammo, that's all. The crap aint very good at causing enough shock and tissue damage.
Many failures to stop? If the rounds mentioned failed to stop a man with a chest hit, it was a rare exception, not the rule. Have you ever seen what a hit from a full military caliber will do to a man's chest? Oh, but then of course you haven't. What time are you going to meet up with Hard Rock?
Gunkid 'thinks' SP 5.56 rounds will make up for his 10" POSCAR. But such rounds will blow up on 'heavy cover', the same 'heavy cover' gunkid 'thinks' he will hid out all day in. So his POSCAR isn't good with ball, and isn't good with SP. Junk, just pure junk.