To date I've not tried any ring/base combo or 1pc that are lower than the old low Weaver Top Mounts w/Weaver bases. Not saying there aren't any out here cause of course I haven't tried them all.
I believe the numbers 260Remguy quotes above are pretty much in agreement with what I have measured. The heights are nominally top of the base to bottom of the scope. (Some sites will give you to the center of the tube, meaning you must subtract 0.5" for a 1" tube to compare "apples to apples.")
How low is low? I have a Pre '64 M70 .30-06. With the Weaver one piece base (#96), Weaver Top Mount low's, Leupold 3.5-10 x 40mm, the objective will clear the barrel (but maybe not the rear sight, depending on the sight), and the bolt will just barely NOT touch the ocular. BUT, if you go with Weaver two piece bases (#46 & #47), even the aluminum ones are just a "leeetle" bit lower, the bolt will touch, and you need to use Weaver medium rings. I assume the one piece base is made a touch taller to give clearance to the loading/ejection port. Steel two piece bases like Warne are a bit lower still, but I think the Weaver medium ring will still clear. Modern M70's give a bit better bolt clearance. Low lift bolts like the Browning A-Bolt are good at the bolt and the objective is all you need to concern yourself with.
Point is, as EZEARL says, they will go about as low as you can go and clear the barrel and bolt.
Best,
Gun Doc
