Hello, I have a Vortex Strike Eagle on my AR. I understand it is a second focal plane scope, meaning the reticle always stays the same size when changing the power of the scope. I understand first focal plane scopes have a reticle that changes size with the zoom feature.

Which scope style is better for an AR type platform? And more importantly, why?

Thanks

Rick

A second focal plane scope has to be set to a designated power for ranging and holdover but with a first focal plane both can be done at any magnification.

If you're not using the reticle to range targets or using hash marks for holdover a first focal plane scope may not be worth the extra expense.

Brad hit it on the head.
Also... How far do you plan on shooting, and what will be your targets, (animal, or just plain "targets")?

Generally speaking...

FFP the reticle always stays the same size in relation to the target regardless of magnification setting on variable magnification scopes. This is good for using the reticle for ranging at different magnification levels. On the downside, some users of FFP scopes will complain that the reticle appears too thin on low magnification setting or too thick on high magnification settings at further distances for their particular use.

SFP the reticle shrinks in size in relation to the target as magnification increases. This can benefit precision shooters at distance because the reticle is covering less of the target. As well, at low magnification levels the reticle is larger in relation to the target which can aid in faster target acquisition at shorter distances. So.... there's a potential positive on both ends of the spectrum. On the downside... any ranging must be done at a specific magnification level.

FFP scopes seem to be gaining in popularity but it has been my observation that very few people are competent at using a ranging reticle. It's one of those things that sounds good but in practice the math is simply more than most are interested in or capable of. There's cheat sheets like Mildot Master and others...

What is best for an AR platform? Well... it's more about the type of shooting you'll be doing. The buyer should first understand the type shooting they will be doing in order to select an optic that well serves that purpose. For me, I have no expectations of my rifle beyond 300yds nor am I precision shooting. I just want a fast point and click aiming device. A simple 1x red dot serves that purpose well.

None of the above information is wrong, but it does need some context and some clarification.

Higher purchase costs aside, there is still no free lunch with a first focal plane scope and you'll ned to determine whether the limited additional utility it offers is worth the losses in other areas.

The hash marks or dots on the reticle subtend the same angle regardless of magnification, which means the reticle gets larger as the magnification is increased, and it gets smaller as the magnification is decreased so that if the hash marks or dots are 2 MOA apart they will subtend 2 MOA regardless of magnification.

At higher magnification the lines on the reticle itself get wider in the scope and at lower magnifications the lines on the reticle get thinner in the scope - because they are subtending the same angle. This can cause two potential problems.

At short range, where you normally use low magnification, the lines will be thinner, and if they get too thin, they are hard to see. The same issue occurs in low light, when you also normally use lower magnification, and those fine lines can disappear against a dark background in both conditions.

Thus, the minimum size of the reticle lines has to be large enough to not disappear on you in low light or at short range against a dark background.

However, thicker lines on the reticle cause issues at long range where you use higher magnification as the lines are now so wide that they can obscure a small target at long range. That's unfortunate, because you have higher magnification in the first place to allow you to see smaller targets at long range.

So at best, the width of the lines is a trade off, and it's more of a trade off in higher dollar scopes where the zoom ratio is 4x or 3.5x rather than 3x, for example, 3x-12x, or 4-14x rather than 3x-9x.

It helps a bit if the reticle is illuminated, but that has its own set of downsides and makes you battery dependent.

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Choosing one or the other then comes down to how you plan to use it.

If you plan to use the reticle for ranging purposes AND you need to be able to do so at the minimum magnification, it might make sense.

Even if you do not use the reticle for ranging purposes, it can still be beneficial if you use the reticle to adjust the hold point at different ranges.

However, in practical terms, about the only application where the upsides may offset the downsides is if you are in a situation where you have to rapidly engage targets over widely varying ranges in minimum time. But even then, the targets need to be such that you actually need to change the magnification in the scope (e.g. you need higher magnification to see them at long range - and they are not so small you cover them with the reticle wires). You also actually need to have the wider field of view at lower magnification to get you on target quicker. If not, you are no better off than you would be with an SFP scope.

On the other hand, in the above application, you can still get much the same utility with very little extra effort. For example, I have a 4-14x (a 3.5 zoom ratio) SFP scope. The reticle hash marks subtend 2 MOA at 14X. 14x produces a fairly narrow field of view, and at shorter ranges it's over kill. However the scope has a convenient dot at the 7x location which makes it easy to accurately set the optic at half power. At half power the hash marks now sub tend 4 MOA. Thus I can range targets and use the reticle to hold off the target at half power, taking advantage of the larger field of view. I just half to remember the subtension of the reticle is 4 MOA rather than 2 MOA.

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Cost considerations arise in two areas. FFP scopes cost more than SFP scopes, and for a given budget, you can get better optical quality with SFP scopes. Fixed power scopes will also offer better optical quality for a given price, and will have greater throughput of light as they have fewer lenses than a variable.

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With respect to an AR and a SFP or FFP scope, it really depends how you've got it set up. If it's a varmint AR with high magnification, SFP makes more sense. Your shots will mostly be at long range, with time to set up the shots, and you'l be putting the elevation and windage on the turrets, not holding on the scope. If you are using the scope to range, you'll be doing it in high magnification, and if you are using the hash marks for windage or elevation corrections, you'l be doing that at high magnification was well. And you certainly do not want to obscure small targets.

If your AR will be used primarily for shooting at close ranges (300 yards of less) you'll be using a lower powered optic. In some cases you might want a variable with perhaps 1-4x, 1.5-4x or 1.5-6x zoom capability.

However, the trajectory change over 0-300 yards is minimal. Even with a carbine length AR and a 62 gr FMJ if you zero at 285 yards (3.6" high at 100 yards) you'll have a maximum trajectory of +5" at 170 yards and you'll be 5" low at 330 yards. In essence, you can aim dead on over the entire range, or make a very minor hold correction on the target, using target size as a reference rather than the reticle subtension. Which is to say, you don't need the capability that the FFP reticle offers.

In fact, unless you are also shooting at very close range, a fixed power 2.5x, 3x or 4x scope will be more than adequate, and SFP versus FFP isn't an issue with a fixed power scope.

That really leaves the need for a FFP scope with the "special purpose" AR where you need the capability to engage targets at both medium/short and long ranges where you might need to adjust the magnification, and also both range through the scope and make initial windage and elevation adjustments using the reticle.

Even then, you can still meet the demands in those environments with a well set up SFP scope using maximum and half power without losing much speed or utility.

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There is however the snob appeal of the FFP scope. They are "cool" and thus people want them even if they don't need them, don't use the features they offer, and are not aware of what they are giving up to have that cool factor.

A more important consideration is Mil versus MOA reticles.

Here again the main driving force is the tacti-cool folks who want to use mil because most military shooters use mils.

There are pros and cons. 1/4 MOA clicks are slightly more precise than 1/10 mil clicks (2.6" at 1000 yards versus 3.6" at 1000 yards). However mil sight adjustments are easier to communicate as it can be done with fewer digits (5.2 mil versus 17.75 MOA). MOA hash marks are more granular and require less extrapolation when determining how much the targets subtends in the reticle. In contrast you usually need a separate ranging scale in the scope to do accurate range estimation with a mil reticle.

Pros and cons and tactic-cool issues aside, the major problem is that using mils many not be in the best interests of most shooters. In fact I've met military snipers who don't use the system to its full advantage.

If you're using a mil reticle for ranging purposes, you need to estimate ranges in meter and estimate target size in centimeters. Similarly, if you use a MOA reticle for ranging purposes, you need to estimate ranges in yards and estimate target size in inches.

In other words, you should select the system that matches how you think. It makes range estimation something you can then do in your head.

When using an MOA reticle:

Range in yards = (target size in inches/target size in MOA) x 100

In other words is the target is 30" tall, and subtends 4 MOA, it's 750 yards away.

Even you can't figure out 30 divided by 4 in your head, you can divide 30 by 2 and divide the resulting 15 by 2 to get 7.5. Or you can divide 40 by 4 (10) and 20 by 4 (5) and then split the difference (7.5). Either way 7.5 x 100= 750 yards.

When using a Mil reticle:

Range in meters = (target size in centimeters/target size in mil) x 10

In other words if the target is 75 cm tall, and subtends 1.1 mil, then the range is 680 meters.

That's a little harder to do in your head, but where it gets really nuts is if you are using a mil reticle, and thinking in yards and inches.

Range in yards = (target size in inches/target size in Mil) x 27.8

30 inches/1.1 mil) = 27.27, 27.27 x 27.8 = 758 yards.

There's no way I can do that in my head, and I'm better at doing math in mu head than most people.

It isn't much easier if you range in meters and estimate target size in inches:

Range in meters = (target size in inches/target size in Mil) x 25.5

(30 inches/1.1 mil) = 27.27, 27.27 x 25.5 = 695 meters.

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In short, don't get sucked into the ad populuum logical fallacy that mils must be better since so many people use it. What needs to matter to you is how you think. If you think in imperial units (inches and yards) then go with MOA. If you think in metric units (cm and m), then go with mils. If you think in one and go with the other, you've just made your life a lot harder and you've pretty much ensured you will not get maximum utility out of the scope.

And what ever you do, be sure that the turret adjustments match the reticle - mil/mil or MOA/MOA. If you get mil/MOA or MOA/mil, you're wasting your money.

WOW! Such great information. This truly is the best website for information on these rifles.

I have my AR sighted for 50 yds, and will probably never shoot more than 100 yards, unless it's for kicks at a long rifle range someday.

With this in mind, and with the trajectory of the AR, I really have no need for hold over or under, and thus do not use the hash marks for ranging purposes.

I seem to be just perfect for my uses with my SFP Vortex. I have no need to be the cool kid on the block with the latest and greatest.

Thank you all, for the terrific information.

Rick