losing velocity in Mark II TR? sanity check

I'm concerned that my barrel is too long for subsonic ammo. This rifle is very very quiet to shoot, and the muzzle velocity seem to calculate out to about 50-150fps below the ammo's claimed speeds (based on measured bullet drop and guessing speeds in a ballistic calculator until find a speed which gives matching drops).

Am I completely off the reservation here? Has anyone else noticed similar effects with 22" Savage rimfire barrels?

You will discover 2 things here. 1- That barrels have their own personalities and some are more accurate that others and some are faster or slower than others. 2- Ammo companies often inflate their velocities, and in the case of subsonics sometimes lower the velocities a bit extra to be sure they stay low in longer barreled guns vs shorter barreled ones. Just some observations.