Just got this back from Dan.

The reason you are getting different readings at different ends of the
bullet is the LGP bullet is tapered being smaller at the base than the
nose.
If you are going for a slip fit you will want your bullet to ride the
land
tops. This is the bore diameter and apparently in your rfile its .500"
If your getting a .511 measurment for the groove diameter that tells us
your
grooves are .0055" deep which seems normal to me.
I would guess that what you will end up with for a useable bullet
diameter
will be .500" to .501" I can do eather or both your call.



I just used the small hole calipers and measured that and it did come up as .500" So i think i'll go with Dan's .501" bullets to be on the safe side