brushbustin
One thing i would remind you is that really are not shooting a 100 grains of T7 since you are shooting pellets. Your load would be close to the equivelent of 100 grain of true BP (other than Swiss it is closer to T7 than any other BP) or Pyrodex. The load would be equivelent of 85 grains of T7.
I think that Semi's estimate of 1600 fps second to be very close to your actual velocity. As an example I shoot a 400 grain Bull Shop conical with 100 grains of loose T7-3f and the average velocity runs right at 1550 fps.
If you are or might sight your rifle in again I would suggest you follow Ron's thoughts and sight the gun it @ 2.5" high at 100 that will easily cover you at 150 to 175.
There still is no replacing making the shots on a target to verify your POI.