1. The 6-24x 50mm has about 12 MOA of reticle-up adjustment, and 52 MOA of reticle-down adjustment from the reticle being centered.  A 0-15 MOA base will work well with a 100 yd zero.  A 20 MOA base might be a few MOA short of reticle-up adjustment.  A 20 MOA base could be zeroed to 300 yds.
  2. With a 10 MOA base and 100 yd zero, there will be about 46 MOA of reticle-down adjustment remaining.  That corresponds to about 1,100 to 1,200 yds for long distance cartridges.
  3. With a 15 MOA base and 100 yd zero, there will be about 51 MOA of reticle-down adjustment remaining.  That corresponds to about 1,200 to 1,250 yds for long distance cartridges.  15 MOA is likely the optimum base.
  4. With a 20 MOA base and 300 yd zero, there will be about 52 MOA of reticle-down adjustment remaining.  That corresponds to about 1,250 to 1,300 yds for long distance cartridges.  When the reticle is placed on target, it will be 4″ (4 MOA) high at 100 yds, and 5″ (2.4 MOA) high at 200 yds.
  5.  If you prefer MOA adjustment to 1,300 yards with a 20 MOA base, you could hold-under at 100 and 200 yards.  Since 1 mil-dot = 3.43 MOA, 4 MOA is just over 1 mil-dot, and 2.4 MOA is close to 0.75 mil-dot.