Oh, you know what, you are correct, the tailstock is slightly high by .0025".
I was wrong. Is .0025" going to kill you on alignment?
Most likely not going to hurt what I need to do.
The barrels come in at 1.020, to be finished to 1.00x from the back of the barrel extension (BE), then it steps to .750 to the muzzle. We use a clamp on gas block. After the chamber is done I will turn the remaining stick out to about 1.007, not critical, I use this to dial in the barrel when I flip it to turn the rest. That short section should be concentric to the bore. Normally with the set thru chuck (in the case of the sample picture, BE was chucked up in the combination chuck) I just clamp on the BE, which is about an inch long, and as mentioned I dial the barrel on that turned section ahead of the BE.
My thoughts it may not be a good idea to just use the front section of the jaws to clamp on the material, thus the reason I wanted to tap that stock with .750 ID so I can have, say a 6 inch extension, long enough for the rest the chuck jaws grabbing on the material.