From my 12" Grendel:
120gr Federal OTM 2384fps 11rd avg
90gr TNT 2683fps 9rd avg
Haven't chrono'd 123gr American Gunner but I'm getting consistent hits at 800yds with it on steel buffalo on multiple range trips, using the magazine as a monopod and a 1-4x scope. 10/10 hits on 450yd 18" steel.
David Fortier's Oehler Chronograph data:
Alexander Arms 12.5 inch 6.5mm Grendel
Alexander Arms 100 grain Berger OTM 2470
Alexander Arms 123 grain Scenar OTM 2330
Velocity figures are 10 shot averages recorded on an Oehler 35P placed 12 feet from the muzzle 1,030 feet above Sea Level at an ambient temperature of 30 degrees F.
grayfox:
"My 12.7 no suppressor, 123 factory custom (sst), 2263, sd-20.2, factory hdy 123 Blk (ELD-M) 2217, sd-10.9"
Great Grendel: 6.5mm Grendel Hornady Black 123gr ELD Gel Test
12" / 123gr ELD-M avg: 2,254fps