Ask most shooters to define minute of angle (MOA) and you'll probably elicit the reply, "It's an inch at 100 yards."
Ask most shooters to define minute of angle (MOA) and you'll probably elicit the reply, "It's an inch at 100 yards." A purist overhearing this will almost certainly chime in with a smug correction to the effect that a minute of angle is really 1.0471996 inches at 100 yards, but if you're numerically challenged and ask nicely, you may round it off to 1.05 inches. As a lifelong nitpicker, I admire the precision the purist brings to the party, but as a shooter I think I'll stick with a simple, useful, rounded-down inch. After all, even at 1000 yards the additional decimals don't quite add up to a half-inch. I, for one, cannot hold close enough at that distance for the discrepancy to matter.
The jaws of the caliper indicate the formal value of minute of angle (MOA) at 100 yards, 1.0471996 inches, allowing for vagaries of operator interpolation and mechanical tolerances. The ruler shows 1 inch, the commonly accepted value of MOA at 100 yards.
The MOA is a useful tool for shooters because it varies in direct proportion to distance. Our nominal inch at 100 yards is a half-inch at 50 yards, 2 inches at 200 yards, 3 inches at 300 yards, and so on. This makes it possible to calibrate adjustments for range and windage on precision iron sights and optical sights in easy-to-use standardized increments of fractional and whole MOA.
A typical hunting scope is likely to have adjustment dials click-stopped and marked at minor intervals of 1/4 MOA with major calibration marks at 1 MOA intervals. A high-power scope for benchrest, target, or varmint applications may have 1/8 MOA adjustment capability. And it's not unusual for red-dot handgun sights to have coarser adjustment intervals of 1/2 MOA or so for convenience at typically shorter handgun distances.
Not all scope adjustments hew to the familiar 1/8, 1/4, 1/2 increments. European optical sights usually feature MOA increments attuned to the metric system. A case in point is the Zeiss Victory Diavari 6-24X 72mm long-range model, which has 1/5 MOA clicks that correspond neatly to a 0.5cm shift in point of aim at 100 meters. Closer to home, I have, and still happily use, an aging Burris pistol scope that was made with 1/6 MOA adjustment intervals.
Most optical sights have adjustment drums or dials marked with click values. The high-power target scope (L) is clicked at 1/8 MOA intervals while the 1.5-6X hunting model (R) has 1/4 MOA clicks. The tiny dial of the red-dot pistol sight (B) is unmarked, but the owner's manual indicates a click value of about 1/2 MOA. As a rule, finer adjustment increments are useful for long-range or high-precision shooting, with coarser clicks easier to live with in close-range, less finicky applications.
Most optical sights have elevation and windage dials marked with the click values to reduce confusion. If you have a sight that doesn't indicate the adjustment increment, write the click value on a self-stick label or snippet of tape and stick it on the sight or firearm. A day will come when you'll be glad you did.
When you shop for an optical sight, make sure the models you consider have MOA click values consistent with your shooting needs. Fine adjustment increments benefit fiendishly precise benchrest and varmint shooters. Coarser clicks are more practical for less hypercritical pursuits.
Personally, I spent a year being driven to distraction shooting high-power rifle silhouette with an otherwise excellent scope that had 1/8 MOA clicks. The elevation drum provided 71/2 MOA per one full turn. I needed 12 MOA from the chicken setting to the ram setting, a trip from 0 for the chicken through a full turn past 0 to 41/2 on the scale for the ram. I trained myself to wind down to the chicken 0 immediately after shooting rams to avoid utter confusion. I finally gave up and replaced the scope with one clicked at 1/4 MOA intervals with 15 MOA per full turn of the drum. A bit of forethought in initial scope selection would have spared me considerable agita. Live and learn.