Ron,
A new front base is "skim"milled on top, but especially in the dovetail cut for the plate. At this point the plate will not fit into the dovetail, so isn't installed.Since the plate comes already fit to the ring, the reason for milling the dovetail is to level the whole assy. and insure it is parallel to the water table.
In boresighting,the chord is only to hold everything together, so you can determine the height of the rear ring.The rifle is not fired, and the scope is not adjusted.The boresighting is done by adjusting the height of the adjustable block under the scope.Since the reticle is centered before boresighting to find the correct height of the ring,maximum adjustment will be avaliable to sight it in, when the job is completed.
There are a couple reasons not to have the feet(in your case foot)bear hard on the barrel.Certainly, dirt/trash is a real concern;but also bearing on the barrel puts pressure on the solder joint between the rear base and barrel.When the rifle is fired in this condition,it "shocks" the solder joint.I have seen a rear base come loose because of this(I understand yours is screwed on).Also, if the feet bear on the barrel,it affects the fitting of the slider to the slot.The reason to have the feet close is for strength.
You are lucky to havs a Tig welder.
Mike
