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Guns & Ammo Network


Minute Of Angle

by Hugh Birnbaum   |  January 3rd, 2011 19

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.

  • Heath Silcott

    Actually, your caliper is reading 1.0047, not 1.047. Maybe you forgot that a machinist might also be in the conversation.

    • Jonsey

      "Maybe you forgot that a machinist might also be in the conversation."

      Well aren't we just all high and mighty! Maybe you forgot that people can make mistakes and a rational person might come and knock you off your high horse. Jackass.

      • Chris

        There's no way you can tell at that resolution, you're just showing off that you may or may not be a machinist.

        • Joel

          Chris, if it were correct, the needle would be on the 47, which is three marks before the 50 on the bottom of the dial. You do not need to zoom it in to see that it is 42 marks off, way back near the top of the dial on the 5th mark.

  • Bob jones

    Are you a Machinist for the Ford corporation or what? Look at it again!! The Dial Calipers that he is using only graduate to .001… That is a standard industry Dial Caliper, Last time I checked, reading to the nearest 0.0001 required a Micrometer.

  • scott

    The caliper reading is between 1.004 and 1.005, so I am sure he was rounding/estimating it to be 1.0047.

    • Joel

      Yes, I am sure he was. However, the dimension that he was trying to portray is 1.047″, not 1.0047″. One does not need to blow up the picture in order to see it is not even close to the 47th digit, which would be three ticks before the 50 on the bottom of the dial.

  • meknowitall

    nope he's right. the dial measures in hundredths. second digit = hundredths. each tic on the dial = 1 one hundredth. I think Heath works for Chevy

    • Heath

      I agree with Heath not because my name is Heath or that im a machinist also but because i like chevy s .lol

    • employer not matter

      each tic on the dial is 1 thou. the scale on the caliper between each inch marking measures in hundreds. .001 or a "mil" thou .01=ten thou .1=hundred thou

      .0007= usually say it as 7 tenths of a thou

    • Joel

      Not so. Each revolution on the dial moves the slide one tenth of an inch. The dial divides that tenth into one hundred increments. That would make each tick on the dial one 1/100 of a tenth of an inch, not 1/100 of an inch. 1/100 of a tenth of an inch is 1/1000″, or .001″. I am pretty sure the same would apply whether Chevy, Ford, or Chrysler. There, now you knowitall.

  • Rick

    I hope he doesn't reload his own ammo. LOL

  • Heath SIlcott

    I was simply stating that the reading of the caliper is about 42 thousandths off from what it states in the photo. Yes, I have been reloading my own ammo for about 20 years and if you are off by .042 you can run into some serious problems. I wasn't trying to be an a$$hole, the Marine Corps taught me to pay attention to detail. After reading the replies here I see that some of you do not know how to read a caliper correctly, so maybe it's a good thing that I did comment. If you want to "knock me off my high horse" just drive to Fort Valley, VA. and ask for me, everyone here knows me and will give you directions to my house.

    • TexSwatt

      Heath, I’m not sure what your trying to prove. I have blown up the picture and as close as I can tell it’s dead on the 1.0471996 as he states. The caliper is in 100ths and is a hair off of 1.05. Plus your math is off. Simple 0.1 is a tenth, .01 is a hundredth, .001 is a thousandth soooooo….. .042 is forty two hundredth and .0042 is forty two thousandth. Must be that Marine Core training and paying attention thing you were bragging about. Hey I trained at camp Lejeune for awhile too, AND since you are such a stickler it is pronounced La Jurne. Now of course that is coming from my Grandfather who was friends with the LG, and my whole family was friends with the Lejeunes. Now of course the Marines have been trying to get you guys to prounce it correctly for a long time. It only took Ms. Lejeune aka Aunt Laura one time in correcting me for me to remember. But the point is you are wrong on what the caliper shows. Now being 42 thousandths off can get you in trouble if your building a sub, a water tunnel but in shooting…not really. Even at 3,000 yards! But you probably know better, you have been reloading for 20+ years and a Marine. Well I have been making and reloading for more than 20+ years and have been saving Marines, especially SEALs butts for nearly the same time frame. (though not the only ones). I digress, next time enjoy the article, don’t start any crap, and DO NOT encourage people to knock you off your high horse. I know people act tough online and I am sure your a bad a$$ but there are many others tougher or crazier than you. I wish you good luck, but try not to fire the flames of a fight. If you can be positive and help those seeking information and you can be correct then please do so. Thank you for your service.

      • Joel

        Thank you both for your service. However, Tex, Heath is 100% correct. The graduations on the slide are dividing the inch into tenths. Each time the dial makes one complete revolution it moves the slide one tenth of an inch. The dial divides that tenth into 100 increments…or one tenth divided by 100, making each one of the 100 marks 1/1000 of an inch (.001″). The calipers read closer to 1.005″ than 1.004″, so that would make them almost exactly .042″ off.

    • Joel

      Correcting a mistake and stating something that is factually correct might make you a bit anal, but it does not make you an a-hole. In your line of work, if you are not a bit anal and pay close attention to detail, bad things happen. You are 100% correct with your assessment. I am sure that Mr. Birnbaum, being a writer and not a machinist, just made an honest mistake…and you, being a service oriented person, just wanted to help him get it straight. Why is it that the idiots have to come out of the woodwork and show their lack of education? I do not know. I guess the “no good deed goes unpunished” rule applies. Anyway, thank you for your service. If I am ever in the Fort Valley area, it would be my honor to buy you a beer and thank you in person. Stay safe.

  • John 5792

    Can someone explain how a rifle can shoot .09 MOA @ 200yds when the bullet diameter is greater than this?

  • John 5792

    I dont get it..

  • Heath Silcott

    John, the only time bullet diameter is important is when you’re measuring the group. Say you fire 3 shots at 100 yards with a .308 and all holes are touching or overlapping. You measure the outside edges of the group and since you are trying to find the center of the holes, you subtract .308 from that. That is your group size. So, if you fired 3 shots into pretty much one hole with a .308 and your hole measures .355, you just fired a 3 shot group that measures .047.

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