What is the chrony you are using? My Gamma Chrony (Canadian) is over 12 years old but still works fine. My friends Pro-chrony reads 150 fps to 200 fps slow now & we both have lost confidence in it.

On the other hand different rifles give variable velocities with same powder charge / bullet combo. My Simson 9.3X62 gives 2450 fps with Lapua Mega 285 gr & 58 grs of AR 2208 (Varget). It also does 2550 fps with Nosler & Barnes 250 gr bullets & 60 gr of AR 2208 / Varget. This is 3 to 4 grains more than the Nosler manual for similar weight bullets & velocity.