Everything Wrong with LPVOs

Addressing the Issues of Low-Power Variable Optics

[Editor's Note: This article originally appeared in RECOIL #51]
These days, carbines equipped with low-power variable optics have become very popular. A good way to characterize these LPVO-equipped carbines is “Cooper Scout Rifle meets modern 21st-century warfare.” It’s important to remember that the origin of this system has martial intent — there has been a disconnect among many shooters, as the original inception of the optically sighted carbine is a little dark and grim.

Even from the early proliferation of optics on the battlefield, the purpose was simple — to enhance the capabilities of the basic rifleman in his/her task.

THE FUTURE IS NOW, OLD MAN

Up until the last 20 years, the progression of the modern carbine hadn’t pushed much beyond World War II concepts. Sure, we did some stuff with polymers and aircraft-grade aluminum for that Indo-China thing, but let’s face it, the Cold War was arguably lame with respect to what actually got fielded in terms of small arms. Until recently, we’ve gone to war with the same sighting concepts our grandfathers did.

The strategic execution of the global war on terror is up for historians to debate, but what’s undeniable is that it has allowed for nearly 19 years (and counting) of non-stop warfighting research and development. The conflict has ranged from peer/near peer engagements to countless ongoing counterinsurgencies. Necessity is the mother of innovation, but a solid nod needs to go to the father, which is foresight. This unholy union provided us with what is arguably the most paramount of small arms innovation: the proliferation of optically sighted service rifles and carbines at a mass level. Enter the Trijicon Advanced Combat Optical Gunsight (ACOG).

[The ACOG] was the biggest improvement in lethality for the Marine infantryman since the introduction of the M1 Garand in WWII. – James Mattis

The crux of the problem is that modern gunfights are increasingly complicated. Most targets in combative engagements are often presented for limited time and/or size exposure. Additionally, targets are increasingly being presented in less than optimal light conditions. Moreover, the emphasized need to properly identify combatants versus non-combatants makes the phase “complicated” sound like an understatement.

While the optically sighted carbine with a fixed 3x or 4x is very effective at intermediate ranges, it’s less than ideal when you’re cohabitating rooms with the opposition. Thus, the birth of the LPVO into modern warfare.

HOW MUCH MAGNIFICATION?

The old sniper rule of thumb you often hear regurgitated is “1x for every 100 yards/meters.” But remember this old-school mindset comes from the dog days of the Cold War; in reality, the opposition tends to reduce their visual signature by using camouflage or concealment. So there’s a new rule: You’ll probably need to go with at least 2x for every 100 yards/meters in the real world.

At this point, we can safely say 1-6x suffices out to 300 yards, 1-8x is good for 400 yards, and 1-10x buys us real estate all the way out to 500 yards. Before you start furiously posting on the internet about this, yes, these magnification ranges can be effectively stretched much further under ideal conditions, but in the complicated nature of gunfighting, conditions never seem to be ideal.

TOO CLOSE FOR MISSILES

The first consideration is fairly straightforward, and some might assume that simply grabbing the latest and greatest 1-10x is the answer (see page 146 for a breakdown of the Vortex 1-10x). Unfortunately, we have few a more points of review that aren’t so readily apparent. While shooters demand a 1x that’s as fast as red dot and a 10x that would put Carlos Hathcock to shame, there are some real limitations to what can be done and for how much money.

We need an effective power range from the outer limits all the way back into “bad breath distance.” Building an optic with a magnification power ratio that can handle that range demands a lot from the engineering perspective. Beyond power ranges, the LPVO riddle muddies quickly into a quagmire of factors, including eye box dimensions, focal planes, and reticle selection.

SORTING IT OUT

This messy trifecta of eye box dimensions, focal plane, and reticle choice dictates the optic’s usability. The “eye box” represents how much you can move your eye laterally and axially behind the optic while still maintaining correct sight alignment and picture. This three-dimensional space is dependent on the optic’s exit pupil diameter, the diameter of the eye pupil, and eye relief. Of course, there are no free lunches — generally speaking the higher the power ratio, the more restrictive the eye box becomes at the top end. A power ratio of 6x will be much more forgiving than 10x.

What does a smaller eye box mean in the real world? The issue you’ll most likely see is that moving the optic and rifle while transitioning or tracking targets at the higher end will become more difficult. Secondly, when engaging from alternate, less stable firing positions, your cheek weld will need to be more consistent and recoil might shift the eye box out of alignment. This compromises sight alignment and makes that extra magnification of the 1-10x something of a liability in a gunfight.

Moving onto focal plane selection, the plot thickens. For those unacquainted, here’s a two-sentence explanation: With a first focal plane (FFP) scope, the reticle scales up and down in size with the magnification level, while a second focal plane (SFP) reticle looks the same regardless of magnification.

SFP optics may be championed by manufacturers because they’re generally cheaper to make. SFP is nice in quick, close-range engagements at the lower end of the magnification ranges. However, it’s a double-edge sword. While SFP reticles stand out better at the low end, in order to use the reticle for elevation or windage holds, the optic must be at maximum magnification or the subtensions of the reticle (the distance represented by the marks in the reticle) won’t be correct.

Given the higher power ranges of the 1-8x and 1-10x, it’s likely that a shooter may not always need or want to use the maximum magnification, which can limit the field of view and the eye box. An FFP reticle eliminates the possibility of a mishap with holdovers, as its subtensions are always accurate no matter the magnification. The downside is that while some reticles work great at 8x or 10x, if they’re too fine, they may become very hard to see at 1x since they change in size. With an FFP scope, you must be careful to select a reticle that’s both fine enough for precision work but bold enough to find quickly when zoomed out. Additionally, if you choose an FFP optic, suitable daylight-visible illumination will greatly aid close-range performance.

The caveat to all this focal plane complexity is that LPVOs with power ranges of 1-6x tend to spend 99.99 percent of their operational life at either 1x or 6x and hardly ever in between. In this case, an SFP can be a fine choice. When considering LPVOs in the 1-8x or 1-10x range, FFP designs have some distinct advantages out at distance.

CAVEAT TO THE CAVEAT

The second caveat regarding focal planes: As awesome as LPVOs are at the low end, red-dots optics are almost always faster — so why not just use both. Thankfully, we live in the golden age of firearm accessories, and you can attach an offset mini red-dot sight as your CQC sighting system. There’s a real smorgasbord selection of rugged MRDS to choose from these days.

Off-axis MRDSs are not only fast and forgiving, but they have the added benefit of always being ready for action. All LPVOs, whether a 1-6x or 1-10x, require you to take a moment and an extra hand to find the magnification ring and rotate it. Even with a throw lever, nothing beats the speed of a slight lift and tilt of the head.

PARALLAX

Parallax is an effect that occurs within all optics to varying degrees. Parallax within the context of optical sights is seen as the apparent shifting of the reticle in relation the target, in conjunction with movement of the eye. In laymen’s terms, excessive parallax creates error in a shooter’s sight picture. How much parallax is presented and the resulting error induced depends on several factors, such as optic magnification and objective distances.

Optics with more magnification generally present more parallax error. This is why most high-power optics have a manual adjustment to eliminate parallax. LPVOs almost all come from the factory with the parallax fixed at a set distance, such as 150 yards. While this compromise isn’t normally a big deal in the context of how they’re used, LPVOs that reach out to 8x and 10x with parallax set at 150 yards may exhibit a good deal (1 to 2 MOA) of parallax at closer ranges. Again, 1 to 2 MOA at 50 yards isn’t a big deal on anatomically correct targets; however, a 1 to 2 MOA error while zeroing your rifle (some BDC reticles are calibrated for a 50-yard zero) will have pronounced effects when you shoot at extended distances.

MOUNTS

Many folks don’t take the subject of mounting their optics seriously enough. The optic mount is an absolutely critical component and not a place to pinch your pennies.

One Piece or Two?
We’ve learned a simple truth over the years: When an AR pattern rifle is properly fitted to a shooter’s correct length of pull, almost everyone will need a single-piece mount with a cantilever to position the optic further forward on the rifle. Many folks try to make a traditional two-piece ring setup fit on the AR receiver, but more often than not it won’t work.

The main body housing of most optics ends up forcing it to be mounted too far back for proper eye relief. In turn, this causes the shooter to compromise their body position. And in case you forgot, proper body position is a fundamental pillar of marksmanship.

Worse yet, some intrepid souls will refuse to admit defeat and attempt to bridge the receiver and the handguard or stack rings on top of risers. While you might be able to shoot some reasonably sized groups with these setups, when it comes to maintaining accuracy you’re fighting an uphill battle against physics if you do this.

To QD or Not to QD
Whether or not you should run quick detach mounts is entirely subjective to your situation. If, for some reason, you’re feeling extra ninja and need your optic to mount and dismount without tools, in less than 10 seconds, then go for it. If you’re willing to haul around a beastly half-inch wrench that weighs a whopping 6 to 8 ounces and are patient enough to take an additional 20 seconds to fish it out of your kit, then the more traditional method of securing cross bolts is perfectly fine.

Many people get hung up on how well the two types of mounts return to zero. Here’s the practical truth:
>> A quality fixed mount (like Badger, Geissele, Knights, Leupold, or Nightforce) using ½-inch cross bolts will almost always return to zero within a half MOA — if you re-torque it to the manufacturer’s specification.
>> A quality QD scope mount will almost always return to zero within a half MOA — if you read the manufacturer’s instructions and properly set the levers to the correct specification.

Read that last part again; it’s important to understand and where most QD mounts get a bad rap.

Are High Mounts Better?
Everyone jumping on this whole “high mount” concept with mounts floating 1.93, 2.04, 2.4, and 4.08 inches above the bore needs to stop and take a chill pill. You’re late to the game, as the mechanics of higher optical planes on an AR platform has been understood since the mid 2000s.

Sure, faster presentations and situational awareness are great — but there’s an important thing called proper cheek weld. Once you leave the 25-yard flat range, you’ll remember why. The real beef is not the height of the optic, but the fact that many seem to forget that if you raise the mount, the height of the stock’s comb needs to go up with it. All the potential issues associated with LPVOs, like tighter eye boxes and parallax, can become exacerbated without a solid cheek weld.

LOOSE ROUNDS

Low-power variable optics have come a long way and can greatly enhance a shooter’s capability in the types of engagements we now face. However, it’s important to understand their strengths and weaknesses and how best to select an optic and configure it for your needs. Take an honest look at the situations and threats that you expect to encounter, examine the considerations we’ve outlined here, and you’ll be able to dial in your modern-day Cooper Scout Rifle.

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