Re: O MOA rail vs 20 MOA Rail - sighting in diff
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Delta271</div><div class="ubbcode-body">I am new to the long range shooting world, and I am building a new rifle, my last rifle had a zero rail, my question is what is the advantage to having the 20 MOA? more adjustment??</div></div>
For clarification, the use of canted bases DOES NOT increase the Elevation adjustment of a scope - it merely <span style="font-style: italic">"shifts"</span> a portion of the scope's Elevation adjustment (20 MOA on a 20 MOA base) from the low end of the adjustment range to the upper end of the adjustment range. <span style="font-style: italic">Remember:</span> The center line of the scope sits 1.5-2.0"+ above the center of the bore, so a fair amount of "UP" adjustment is used when zeroing a rifle with a 0 MOA ("flat") base, which reduces the amount of remaining "UP" adjustment.
Canted bases angle the front of the scope downward so that the scope's line-of-sight (LOS) and the bullet's point-of-impact (POI) merge. This reduces the amount of "UP" adjustment required to zero. This "extra" 20 MOA of Elevation adjustment can help extend the range of the useful range of the rifle.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Delta271</div><div class="ubbcode-body">... and do you have to sight in or range it differently, when using the mil-dot is your calculation different than the zero? </div></div>
If you don't turn the scope adjustments back to the factory settings when you change from the 0 MOA base to the 20 MOA base, as <span style="font-weight: bold"><span style="font-style: italic">gstaylorg</span></span> said - you will likely be high before you re-zero. Other than that you zero the rifle as usual. Your drop calculations will remain the same - 20 MOA of cant is only 1/3 of one degree, which has very little effect when plugged into ballstics calculators such as the <span style="font-weight: bold"><span style="font-style: italic">
JBM Small Arms Ballistics Trajectory Calculator </span></span>, as well as in the real world.
Keith