Minute of Angle (MOA)

IN THEORY: 
The basic formula for Minute of Angle (MOA) in sniping is 1.047 inches at 100 yards, or for practical purposes, 1 inch at 100 yards. For every 100 yards the bullet travels, you add 1 inch of inaccuracy.

IN REALITY:
A sniper's most valuable classroom is the firing range. Snipers don't have time in the field to think about theory. Hours at the range help snipers to apply these principles by "feel." The greater the distance the sniper is shooting from, the lower the accuracy, as natural forces like wind resistance work on the bullet while it travels through the air.

(SOURCE: How Military Snipers Work by Robert Valdes)
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UDMC CONCLUSION:
Just because your rifle is shooting at 1-MOA at 100 yards does not mean that it will be shooting at 8-MOA at 800 yards. That is theoretically correct but, ask any legitimate sniper and he will tell you it does not happen that way no matter how accurate your sniper rifle is. :)

In the picture is UDMC's S7-PVAR in caliber 7.62 x 51mm NATO.