some good comments you make--and they show experience.
i've been setting rings and mounting scopes since the early 1970's. in that time one does discover a few things about the craft. i learned a few hard lessons early on--ring marks, scope slippage, etc.
since the mid 1990's, when i began using a carpenter's square (which lead to the developement of the Scope-Tru), i've set quite a few rings, many, many of them dual dovetail (leupold brand only), and have shot some of those guns for several years. in one case, a carbine .308, but in each and every case, whenever i've removed the scope for examination, there has never been a ring mark, nor a trace of the scope ever having been mounted. i mention this in my feature article on accurateshooter.com (this is with leupold brand dual dovetail and standard style rings. weaver and rugers rings often leave marks, no matter how careful the installer--weavers apply uneven pressure, and rugers are rather sharp, and the steel is harder, so lapping them in can be difficult). while some may think this impossible, this is in fact the case in the mounting jobs i've done over the past 15 years.
but, a poorly machined ring will cause marks for sure, and qc has been slipping in recent years. i still find the leupold's to be good, but i find i need to examine each set before purchase...
a specific rifle i mounted dual dovetails on last month came out 3/4 inch off of mechanical center at 100 yards--not perfect, but very good for a hunting rig. scenarshooter just set a pair of dual dovetails on his sako using the scope-tru, and he came out at 12 o'clock on windage, 4 inches high--but like me, he's been doing this 40 years--and is ultra particular to do a perfectionists job...
while somewhat premature, some early data on the average of several mount jobs, as done by several different installers--is that the Scope-Tru is acheiving line-up of ring axis to bore axis resulting in a range of "zero to 1 1/2 inches off" of mechanical center at 100 yards. most of mine are 3/4 inches or less...
