Probably a "globos" (sp?) breastplate. It is meant to round away from the body for air circulation and to deflect blows on the curved surface. The hole is a "bullet-proof", which armorers would use to show how close a gun would have to be to hole their best armor. Most times these holes aren't large enough to actually admit the bullet. It was a sign of the quality of the armor.
Well, I'm not an expert on armor, but as I recall it's rounded at the belly and not at the shoulders, and the hole goes all the way through.