I recently used a chronograph to check the muzzle velocity for my SPS Tactical 308 using Federal Match King 168g ammunition. The average velocity at about 10 feet from the muzzle was 2475 fps. This ammunition is rated at 2650 fps and I was wondering if this difference is primarily due to the 20 inch barrel? Has anyone else used a chronograph with this rifle and seen similar results (a roughly 7% difference)? Also, do you think this difference would be comparable when using other types of ammunition having similar weight(mass)?