Here is a link from 2016 where a forum member and I chronographed 16”, 18”, 20” and 24” 6.5 Grendel AR-15’s with a Magneto Speed Chronograph. These velocities are comparable to what can generally be expected. Some barrels are faster and some barrels might produce lower velocities than our barrels. Different lots of ammo can also produce different velocities from lot to lot.
http://www.65grendel.com/forum/showthrea...ph-results
http://www.65grendel.com/forum/showthrea...ph-results

