If your looking for a 6.5mm/ .260 caliber the 6.5 Creedmoor is the caliber of choice for your semi auto AR10 platform. The benefits over the .260 Remington are a shorter fatter case with near equal volume. This allows longer heavier bullets to be at a 2.8" magazine length without taking up powder space. The 6.5 CM seems to function and feed very well due to its shape. By far the best long range choice for a semi auto rifle.