I'm running an 18" Alexander Arms barrel with the 123 Amax, 28.5 grains of 8208XBR and average 2450 fps suppressed. Hornady claims on their website with 2580 fps with a 24" barrel. I did shoot a 1.5" group the other day at 500 yards off a bipod and rear bag. I think the Grendel is a very efficient cartridge for the AR platform. My 18" Grendel with a Vortex Pst 4x16 weighs 9.8 lbs. My 16" LMT 308 with the same scope weighs 11.8 lbs. Hopefully I will find a 6.5 Creedmoor barrel for my LMT and I will be able to run the Amax 400-600 fps faster.