Hi I bought some ammo at a local gunstore it is Sellier and Bellot and the box says .223 reington (5.56x45mm). My question is is it .223 or 5.56? the headstamp says 5.56mm. I asked 3 different employees in the store and they say it is .223 remington and it says 5.56mm because that is the european designation and that it is loaded to .223 Remington specs. Any one else tried this, my barrel is .223 remington stamped S&W M&P 15i and I want to be sure , thanks.
