When you turned the oil pump with the drill did the drill maintain the same speed and counter-rotating pressure or did you experience a considerable drag down on the drill as it started pumping? If there was no change it is likely the pump was fully primed. If the pump was not fully primed you should feel a significant difference in the force on the drill once it starts to pump oil.
If the pump appears to be primed I would temporarily attach another oil pressure gauge as close to the block as possible and see what that says. If you want to try that and do not have a gauge let me know and I will try to find one you can use.
Chuck
