We love Winchester’s 5.56x45 M855 ammunition. Not only is this a great case of ammo to have on hand for plinking and target practice – it’s also useful for home defense thanks to its special full metal jacket projectile. This round’s 62 grain FMJ is known as a “penetrator.” That’s because the front half of its core is made of hard steel instead of soft lead. The penetrator bullet also does a much better job of puncturing sheet metal.