The FFP (first focal plane) reticle is the preferred choice for long range shooters because the reticle grows and shrinks as the scope’s zoom goes in and out, in contrast to second focal plane (SFP) reticles whose reticles stay the same no matter what the magnification.
While SFP reticles are well suited for low power variable optics such as the Firefield RapidStrike as well as medium range scopes such as the Core HX, a shooter with a precision rifle who really wants to “get out and touch” whatever he’s shooting at a thousand yards away would be better off with a first focal plane reticle. This is because a scope with an SFP reticle only has accurate readings at its highest magnification, while a first focal plane’s reticle readings are always accurate, whether the target is 100 yards, 500 yards or 1000 yards away.
But what use would an FFP’s reticle readings be if the shooter has no idea how far away the target actually is? If someone eyeballs the distance on a magical thirty point buck with a white coat, fiery antlers, and the winning lottery numbers stenciled on its backside and misses, it’s very likely the particular someone will end up either destroying his optic in justified rage or going on a Herman Melville-esque journey through the woods for decades. For this, mathematics comes to the rescue.
First, we must determine the type of reticle our scope is using. Scopes use either milliradians (mils) or minutes of angle (MOA) on their reticles. Both of these units of measurement measure arcs around a circle. In the most basic language, mils use the metric system, and MOA uses imperial. Even though it’s possible to use both metric and imperial with the milliradian system, it’s easier to remember this way.
Before anything else, it is extremely important to make sure your scope has matching adjustments with your windage and elevation turrets. You can find this out by reading your scope’s manual, or if purchased second-hand, by calling the manufacturer. There are some bootleg scope companies that switch them around, making MOA reticles with milliradian scopes or vice versa.
Now there are 6,283 milliradians in a circle. This is because a circle has 6.28+ full radians (the formula of a circle is 2πr), each one composed of a thousand milliradians.
2π = 6.28318530718 (number of radians in a circle)
6.28318530718 radians x 1,000 (to convert to milliradians) = 6,283.
In the same way, there are 21,600 (60 minutes x 360 degrees in a circle) MOA in a circle.
To measure your distance from your target, the very first thing you need to do is to line up your target with the base of your reticle and count the number of hash marks or dots until you reach its shoulders – in the case of four legged animals, at least. The number of marks your target occupies is your measurement in mils or MOA.
In practical terms at 1000 yards, 1 mil = 36 inches (1 yard), and if you know how large your target is, you’ll be able to accurately determine your range with an equation. For example, if you know the average white tailed deer is 36 inches tall at the shoulders, and your subtension lines are 1 mil apart, then if your deer appears one mil tall on your subtension lines it’s approximately a thousand yards away. If it fills two spaces, it’s about 500 yards away, if it takes up three, it’s about 333 yards away and so forth. To determine this, we use the formula below:
The common factor here is a distant object with a known size. Generally speaking, rabbits stand up to eight inches tall (0.22yds), coyotes stand at 18 inches (0.5yds), hog stand at 24 inches (0.66yds), deer are 36 inches tall (1yd), and elk are 54 inches tall (1.5yds). Therefore, an elk taking up one and a half mils on your milliradian scope reticle is a thousand yards away.
An alternative way of measuring distance by using inches is through the following formula:
Using our elk friend again, if he stands at 54 inches, we multiply that by the conversion factor of 27.77 to get 1499.58. Divide that number by the number of mils he takes up in our reticle (1.5) and we get 999.78, rounded off to a thousand yards again.
Now, for MOA, we have the same problem to solve, just with different measurements. The MOA system likes working with inches, and if we assume 1 MOA = 1 inch at 100 yards, this system should be easy to understand. Once again, we must be aware of the target’s height.
Let’s go back to the 54 inch tall elk. He takes up 5 and a half MOA worth of space in our reticle, so we multiply his height by 100 to get 5400 and we divide that by 5.5 to get 981.82. Why is the math so different? Remember, there are more minutes of angle in a circle than there are milliradians. If you want to have surgical precision, you should know 1 MOA is actually 1.04 inches at 100 yards, and you should be multiplying by 95.5 instead of the full 100.
Even though you now know the formulae for determining range in both mil and MOA, you might still be disappointed because you are one of the poor unfortunates with an MOA scope and a mil reticle or vice versa. Math can save you again. To convert from mils to MOA, multiply the mils by 3.5. To convert from MOA to mils, simply divide the MOA by 3.5.
If this is all too much math to take in and you’re worried you’ll forget the formulae, you can simply write them down and place them in a cheap shooter armband sleeve ($32 on Amazon) for quick reference. A reminder to those who use SFP reticles: these numbers only mean anything to you at maximum magnification. For you first focal plane reticle users, you’re good to go. Your reticle readings will always be true at all ranges, and your scopes are purpose designed for long range precision shooting.