120 mkz

I'm seeing some strange velocities reloading 120 MKZ with A2200 powder. for example, a three shot string @27.4 grains COAL 2.295" once fired Hornady brass and Federal Match AR primers gives me: 1. 2631 FPS 2. 2563 FPS 3. 2506 FPS The group was the best so far at 1.16". The first shot...