dan, I can only assume you are making a reamer to fit your dimensions. If so, the best thing to do is seat a bullet in a case (you don't need to improve it) so that it fits and feeds from your mag and action. Do all the neck prep (neck turn, trim etc) you want in the finished rd.
Send a couple of these 'cartridges' to the reamer manufacturer. They will take the neck and throat dimensions off the case. Just tell them you want to be a few thou off the lands and whatever clearance you want around the neck. They will understand. For hunting, hard seating is not a great idea.
If planning on using 250 to 300gr MK, I would suggest a 1.5deg leade. The shallower the better. Most reamer manf default to 2.5 or 3 deg. That abrupt of a leade can up your pressures when using long bearing surface/ogive bullets.
If you are using a reamer the gunsmith already has, you are stuck with whatever is dimensioned in the reamer now.
From playing with a variety of wildcats and designing my own, I have 'discovered' that as long as the bullet fully engraves into the lands BEFORE leaving the case neck, accuracy can be very good.
From the above posts of tuning bullet seating depth, no mention is made to adjusting the powder amount. By moving the bullet back and forth, you also change the combustion chamber thus affect pressures.
You can mimic that effect by simply moving powder increments by 2 tenths. As long as the ammo runout is very low and the neck tension high enough to properly hold the bullet during field use, this adjustment of powder will accomplish the same thing as changing bullet seating depth for most bullets.
Some VLD bullets need to be hard seated but I doubt you will be using any of these hunting.
When calc your dimensions of your reamer, take into account that while hunting your ammo can get wet and dirty. Additional clearance around the neck will add a measure of safety to your rifle.
Jerry
