I looked at the specs for different scopes and found numerous specs for what a 'click' of the turret does. One was 1/4 MOA per click, one was 1/4" inch per click at 100 yards, and that 100 yards is critical in this spec. Another was 0.1 MIL per click. Another was on a tactical scope that had a spec of 1/2" per click at 100 yards, and again the 100 yards specification is necessary. And yet another with 1/4 and 1/2 MOA clicks. So what does all this mean and how do we use it?

The following three posts are to explain how the various scope configurations impact sighting in a scope. It will not address range estimation using the reticles. If there is interest in that, I'll do a separate thread about how that works. So here's the first discussion.

Sighting in a scope spec'd for 1/4" per click at 100 yards.

The 1/4" and 1/2" @ 100 yards type specs are the most straightforward so that’s a good place to start. The turrets on a scope have detents and each detent or click changes the POI (point of impact) by a specified amount. The numbers, i.e. 1/4" and 1/2", are the amount the POI is changed for one click of the turret at 100 yards. I mentioned earlier that the 100 yards was critical for this method of specifying scope changes. The 1/4" (and 1/2") is only true at 100 yards, but the spec can be used for other ranges, especially 25, 50, 200, etc. It can also be used at any range but the numbers are not as easy to work with.

There are two ways to determine how many clicks are needed to adjust the POI to the desired POI: one, use a table if you have one or can find one, or two, use some simple calculations.

For submultiples (25 & 50 yards) and multiples (200, 300, 400, 500, 600 yards) of 100 yards, the numbers are pretty easy to calculate. You can pretty much do it in your head. If the ranges are not submultiples or multiples of 100 yards, the numbers get a bit unwieldy but the same method applies to both – one is just more intuitive and easier.

Here's an example of how to zero a scope with 1/4" per click at 100 yards using calculations. I'm at the range to sight in a scope at 100 yards. We’ll assume the scope is close enough to be on paper at 100 yards and I’ll talk about what to do if it isn’t later.

I place my target at 100 yards and fire two or three shots. I find that my group is tight but I’m 2-1/2” low and 1-3/4” to the left. What do I do? I can adjust my scope’s elevation and windage by trial and error by adjusting and shooting until I’ve walked the scope into zero, but that’s time consuming and can take a lot of ammo, especially when both elevation and windage are off. So instead, I’m going to take advantage of my scope’s adjustment clicks and some intuitive math to speed the process up.

My scope changes the POI 1/4" per click at 100 yards so I just need to determine how many clicks I need to adjust the elevation and windage to zero.

For the elevation, I’m low by 2-1/2” so I need to divide 2-1/2” by 1/4” per click. That will tell me how many clicks to change the elevation by. An alternative to dividing per se is to realize there are four clicks per inch of elevation, so to get 2 inches, we would need 8 clicks. That would move us up 2”. Then we need two more clicks for the remaining 1/2” for a total of ten clicks and that should put us right on with the elevation. You would get the same thing by dividing 2-1/2” by 1/4” per click.

Now for the windage. The windage is off by 1-3/4” but we use the very same process. We either divide 1-3/4” by 1/4” or we again realize there are four clicks in one inch and 3 clicks in 3/4” for a total of 7 clicks.

So with only two or three shots, we’ve theoretically zeroed our scope. All that’s left is to fire two or three shots to verify the correction. If it’s on, we’re done, if it’s not on zero, we fine tune the very same way we did above. But, the first adjustment should zero the scope. Sometimes we mis-measure or miscount clicks, so it’s always good to confirm zero with a couple of shots.

What about yardages besides the nice, easy, clean 100 yards? Well there are two cases: one where you are at a submultiple or multiple of 100 yards, and two, where you are somewhere in between multiples.

In preparation for my pig hunt, I knew I wouldn’t be making shots over 50 yards so it didn’t make sense to have my gun sighted in for 100 or 200 yards, so I decided to sight my scoped bolt rifle in at 50 yards and my AR equipped with an Aimpoint Pro at 25 yards.

If your scope won't shoot on paper at 100 yards and you want to zero it for 100 yards, you can start at 50 yards or even 25 yards and move the target out after you zero at these shorter ranges - that should get the POI on the paper at 100 yards. This is the method you'd use:

I set up my target at 50 yards and fired two shots and had a tight group, but the group was low by about 2-1/2” and wide by about 2” (the scope had only been bore sighted). So now, at 50 yards, with a 1/4” per click scope, I have to calculate clicks just a bit differently. One click at 100 yards would move the POI by 1/4”. Since 50 yards is one-half of 100 yards, my click value will also be half as much, or 1/8” per click at 50 yards. From here, it’s the same process as before – determine the clicks, make the adjustments and fire two or three verification shots.

So for elevation I need to go up by 2-1/2”. So there are eight clicks per inch this time instead of 4, so in 2 inches there would be 16 clicks. Then for the remaining 1/2”, four more clicks would be required for a total of 20 clicks.

For windage, I need 2” so that would be 16 clicks and all that’s left to do is two or three verification shots.

When I sighted in my Aimpoint, I was off by about 1-1/2” low and 1-1/2” right. Since I wanted it to be ‘on’ at 25 yards, the distance from the blind to the feeder, each click would be change the POI by 1/16” – 25 yards is one-fourth of 100 yards, so the clicks would be one-fourth of a quarter of an inch or 1/16” per click. I then followed the same procedure as above.

Before we move on to MOA type scopes, let’s do one more example where we’re not using a submultiple or multiple of 100 yards. Let’s say, for whatever reason, we want our scope zeroed at 70 yards. How do we do that? Really, it’s just like before except we have a bit more difficult numbers to deal with. Let’s use the POI at 70 yards as 1.5” high and 2” left.

Like the previous examples, we have to determine how much each click changes the POI at the desired range, 70 yards in this example. We actually do the same thing, but it’s just a bit more ‘formal’. The value per click is obtained by dividing 70 by 100 and multiplying result by 1/4”:

One click = 1/4” x 70 / 100 (I multiplied by 1/4” first – it’s a simpler expression.)

One click = 1/4” x 0.7 = 0.175” per click

Well, I warned the numbers weren’t so clean outside of submultiple/multiples of 100.

Ok, so how many clicks are needed to change the elevation POI by 1.5”? This time dividing is probably the best method:

1.5” / 0.175” per click = 8.57 clicks ??? How do we deal with a fraction of a click? Well we either have to go up or down to the closest click, in this case we’d be closer to 9 clicks.

Same for the windage:

2” / 0.175” per click = 11.43 clicks.

This time the closest integer number is 11, so we would use 11 clicks.

So that’s how the 1/4” at 100 yards type scopes work and the same thing applies to 1/2” at 100 yards except of course you use 1/2” to do the calculations instead of the 1/4”.

In the next post, I'll discuss how the MOA works...