I'm no gunsmith but what you are looking for is a torque driver. As far as I'm concerned it is the only way to assemble a gun, mount a scope or do anything that requires consistent assembly.

First of all the Fat Wrench is junk. Not repeatable and no precision at all. I use a Wera, it cost about $80-$100 and it is calibrated to a National Standard as opposed to some chinese kids best guess.

Aluminum scope rings 12-15 in lbs. depending on quality. Steel rings slightly more..like BB said 17-18 in lb.

If you mount one this way you will never mount another without a torque driver.