So what? Lots of calibers work in standard AR rifles. Here’s what’s special. The 224 Valkyrie uses longer and heavier bullets, usually about 90-grains compared to the standard 55 of .223 Remington. That means they carry velocity over longer distance, drop less, and are less affected by wind. In fact, depending on conditions and altitude, the bullet can remain supersonic out to 1,300 yards.