I don't know why this finally occurred to me after more than half a century of shooting but here goes.
When I mount a scope on a bolt gun I generally use mounts which allow for gross windage adjustment by means of opposing screws on the back of the mount. I make sure the reticle is centered horizontally (generally by the counting clicks method), mount the scope and adjust the mount until the point of impact is centered windage wise. I then lock down the mount and make any further fine adjustments with the scope. With a MSR or other rail system I purchase a good scope mount and hope for the best. So far I have had decent luck. As to the elevation... I adjust it for the desired point of impact and had never given it any more thought. Until yesterday...
I have a new Leupold VX6 7-42X - 56 mm scope which Leupold sent me in exchange for (originally) two FX target scopes which had a design deficiency which they have been unable to resolve. That was the story of another thread. The ultimate home of this scope will be a Fulton Armory FAR-308 PVR-L rifle. In the interim I mounted the scope (using a Mk 6 IMS also provided by Leupold) on a .223 AR platform rifle so that I could get some experience with the scope using more economical ammo and to do some development on my home made "ergonomic-ized" A2 stock. I also want to see what the 16" Lothar Walther barrel on the rifle is capable of. It normally sports a 1.5 4X mark AR scope. Not exactly the thing for shooting groups. To continue...
I found that the elevation adjustment on the MK6 was turned all the way down as it came from the factory. It has a micrometer type scale ranging from 0 - 570 which represents 570 1/8 minute clicks or a little over 71 MOA of elevation adjustment. Interestingly the Leupold web site says the scope has 55 MOA of elevation adjustment - I will have to ask my contact which is true. With the scope regulated to 100 yds I find that the elevation is at 367 or about 10 MOA above half way. the Mk AR was also set somewhat above mid way as far as elevation. Which got me wondering...
When I set an A2 iron sight I start with the rear sight a few clicks off bottom the adjust the front sight to give me a 6 O'clock hold on a 5" bull at 100 yds. This allows me to back down to point of impact = point of aim and/or to adjust for ammunition variances. It is the UP adjustment which will be most useful when shooting from a longer range. Except for the two situations described I would not go BELOW my starting point and certainly not by much.
All of which makes me wonder... Why would I not want my scope similarly set. With a LITTLE downward adjustment and MOST of the available adjustment UP?
TIA,
Ken
p.s. At the moment my range is limited to ~300 yards so this is really an academic/theoretical question. Still, my inquiring mind would like to know
p.p.s. An update on my math
It was late last evening when I was studying the MK6. Actually the micrometer readings are base 8. 1 = 8 clicks, not 10. So the max of 57 is nominally 57 minutes of adjustment - closer to the 55 listed on the Leupold site. That said - the question stands. What is the benefit of giving up half of my potential elevation adjustment?