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Riflescope Selection for AR Variants: Introduction

Every once in a while I go over my correspondence for the previous few months to see if there are any apparent trends in the questions I get.  As far as riflescopes go, one thing is apparent: I field an ever increasing number of questions on proper scope selection for the various AR-type rifles out there.  Now that I think about it, this is hardly surprising.  ARs (also known under a politically correct and, in my opinion, a little bit silly term MSR: Modern Sporting Rifle) are everywhere and come in a dizzying variety of configurations, weights, and calibers.  Similarly, intended uses vary considerably ranging from basic plinking to home defense, to hunting, to varminting, to precision shooting, and so on.  Because of that I found myself suggesting a similarly dizzying array of sighting systems from miniature red dots to long-range precision scopes.  With that in mind, I figured that it is worth my while to categorize different AR rifles according to use and configuration and come up with both general and specific recommendations on the appropriate sights for them for a variety of budgets.  I will also insert some commentary and recommendations on mounts where appropriate.

First of all, let’s consider the different AR types out there, starting with the action size and chambering.

There are two basic action sizes for the ARs.  I will refer to them as AR-15 and AR-10 which is not strictly speaking correct, but is short and easy to type.  The actual names vary with the manufacturer, but as far as I am concerned an “AR-15” implies an action length originally designed for a 223Rem or 5.56x45NATO chambering, while “AR-10” refers to actions that can fit larger 308Win or 7.62x51 cartridges.  Technically, there are a couple of different and not completely compatible standards for 308-size AR rifles: Armalite-based and DPMS-based, but there is no real difference between them from a riflescope selection standpoint, so I will call them all AR-10s for the sake of simplicity.

Both action size have been adapted to a variety of other calibers, but those calibers have to fit in the overall dimensional envelope of either 5.56x45 or 7.62x51.

Technically, there are some even larger AR-style rifles out there chambered for 300WM and 338LM, but they are very few in number and very specialized, so I will ignore them for the time being.

The original AR rifle was designed for the 7.52x51 chambering and sized accordingly; however, since the military was looking for a select fire rifle in 5.56x45, it was quickly downsized to fit it and that is still the most common chambering for an AR-15.  However, since 5.56x45 and its civilian sibling 223Rem were originally designed as varmint cartridges, their sporting use is limited. 

Additionally, the arguments about stopping power of 223Rem have been going on long enough to create a whole market segment for AR-15 rifles chambered in other calibers.  The action size limits how long and how wide those other calibers can be, but there are still quite a few out there.  Here is a partial list of AR-15 chambering (these are the ones I can remember off the top of my head), but I am sure there are others out there that I forgot about:

  1. 5.56x45/223Rem: this is the original AR-15 cartridge which has undergone a tremendous amount of development since it was first introduced.  There are factory loads out there with bullet weights ranging from 40gr varmint bullets to 77gr match/precision bullets with everything in between.  This is still a pipsqueak caliber, comparatively speaking, but with the right bullet I find 5.56x45 to be both accurate and effective.  My 5.56 rifle is set up for 75gr and 77gr bullets and I am comfortable hitting targets out to 500-600 yards with it. 

  2. 204 Ruger is dimensionally similar to 5.56x45, but uses a smaller 0.20” caliber bullet intended primarily for varmints.  A heavy barrel AR-15 chambered for 204Ruger is probably the most effective varmint rifle in the AR family.  It works with standard AR magazines and bolts.

  3. 6x45 is a rather popular wildcat chambering that takes a basic 5.56x45 case and expands it a little to use a larger 6mm bullet.  The primary advantage of this chambering is the ability to use heavier bullets that are more effective on big game and work a little better out of short barrels owing to larger expansion ratio. It uses standard AR magazines and bolts

  4. 6.5 Grendel (and the nearly identical 264LBC) is an attempt for a true general purpose AR-15 rifle that can be configured for anything from CQB to long range.  I have a 6.5Grendel rifle and it can reach out to 900-1000 yards with exterior ballistic similar to 308.  It is probably the best balanced of AR rifles and make for competition hunting and competition round.  It uses customized magazines and bolts.

  5. 6.8 SPC is Remington backed cartridge originally developed in the Special Forces community by people who have been looking for something with higher lethality than military issue 5.56x45.  It has seen very limited use in the military world, but I see it used by hunters more and more, on game that is seldom tackled with 5.56.  This cartridge had a bit of a rocky start, but seems to be reasonably well established now.  It is at its best within 500 yards and a lot closer than that for big game hunting.  It uses customized magazines and bolts.

  6. 7.62x39 is an AK-47 round that is occasionally chambered in AR-15s.  Technically, the tapered shape of 7.62x39 makes a poor match for the geometry of an AR-15 action, but there are a few of these out there.  Still, in the AR world, the 7.62x39 has been largely superseded by the next cartridge on my list.

  7. 300 Blackout (and the nearly identical 300 Whisper) is effectively a shortened 5.56x45 case necked up to accept 0.30 caliber projectiles.  It is sometimes referred to as 7.62x35.  It uses standard AR-15 magazines and bolts and accommodates a variety of chamberings ranging from 110gr bullets that nearly replicate 7.62x39 ballistics to heavy subsonic loads that push 240gr bullets at moderate speeds.  In its subsonic guise, this caliber works exceedingly well with suppressors.  This round is backed by Remington among others and is well positioned to thrive in the future.  I do not have one of these yet, but I fully intend to get one when the current craziness subsides.

  8. 30AR is Remington’s attempt to create a 30 caliber hunting cartridge for an AR.  I suspect that this will go the way of the dodo before too long.

  9. 7.62x40 Wilson is a cartridge designed primarily for hunting and is likely to exist for some time among the Wilson aficionados.  I will be surprised if it ever reaches significant popularity.

  10. The thumpers: 458 SOCOM (on my list of rifles to acquire), 50 BEOWULF and 450 Bushmaster.  These cartridges loosely approximate the ballistics of classic leverguns chambered for 45-70.  In the grand scheme of things you can load the good old 45-70 a fair bit hotter, but the comparatively diminutive AR “thumper” rounds are not that far off.

With AR-10 the chambering choice is a little more uniform, since this platform is generally not as popular.  However, pretty much any cartidge loosely based on the 308Win case can be (and has been) easily adapted: 243Win, 260Rem, 7mm08, 338 Federal and so on.  However, 308Win/7.62x51 account for the vast majority of AR-10s out there.

With the chamberings out of the way, let’s touch on the configurations and applications.  None of these are  set in stone and some configurations allow for a great variety of uses.  Still, I have to classify them somehow:

  1. Lightweight carbine.  These are typically AR-15s of some sort that look like the M4s used by the military.  There are some AR-10s configured in this general manner, but they are at least a pound or so heavier since the rifle is inevitably more massive. Typical chamberings are 223Rem/5.56x45 and 6.8 SPC in AR-15s, while the AR-10 is usually 308Win.  Barrel length usually works out to be right around 14.5” or 16”, often with a permanently attached flash hider.  These rifles are, in principle, intended for home defense, but they are most often used for plinking and the sighting systems reflect the fact that potential engagement distance is not very long.

  2. Mid-to-heavy weight precision carbine.  These rifles are just as compact as the lightweight carbines, but are a fair bit heavier owing to the thicker barrel made with precision in mind.  Recce barrel profile is a good example of something used in these rifles and they invariably come with free-floated handguards.  Until comparatively recently, this class of rifles did not exist, but it is growing in popularity.  These are somewhat general purpose weapons since they are maneuverable enough for CQB, while allowing very precise fire when called upon.  They cover the same engagement distances as the lightweight carbines and extend it further out to 400-500 yards as necessary.  The sighting system therefore, should be versatile enough to cover a variety of ranges and be a “jack of all trades”, so to speak.

  3. SPR rifle with its heavy 18” barrel came out of a military project that asked for an accurate heavy barrel M-16 variant optimized for firing heavy 77gr bullets to an effective arrange often exceeding 600 yards.  While technically this rifle is only marginally longer and heavier than a precision carbine, in practice the sighting systems are quite different and the scopes used are really focused on precision fire at fairly extended ranges.  That does not mean that the short range use is irrelevant and the rifles are often set-up to allow for CQB; however, the overall emphasis of this rifle is precision at extended ranges (by AR standards) in a compact package.  Hence, the sighting system has to be selected with both precision and flexibility in mind.

  4. General purpose AR is typically a rifle with a 18’’ or 20” mid-weight barrel.  This is a pretty common configuration for both AR-15s (chambered for 5.56x45 or 6.5 Grendel) and AR-10s.  The original M-16 was equipped with a 20” barrel and since the rifle overall is very compact, there are quite a few of them out there.  These rifles are used for plinking, hunting, predator shooting (usually accurized) and a variety of other tasks.  The longer barrel is helpful for hunters since the bullet has a little more velocity, while the rifle is still reasonably handy and lightweight.  Scopes for these rifle are usually not too dissimilar from regular hunting scopes, although there are, of course, some additional considerations specific to ARs.

  5. Heavy varmint rifles are typically AR-15s with bull barrels of 20” to 24” in length chambered for 223Rem or 204Ruger.  Oddly enough, ARs make superlative varmint rifles and there are a lot of them out there equipped with large high magnification scopes.

  6. Long range precision rifles are more typically built on the larger AR-10 action chambered for a variety of cartridges from 308Win to 260Rem and some others.  However, AR-15s chambered for 6.5 Grendel and equipped with long barrels acquit themselves admirably out to a 1000 yards or so.  Scopes best suited for these rifles are often large and heavy and lean strongly toward the tactical end of the optics spectrum.


In the subsequent installments of this article series, I will expand a little more on appropriate scopes for each one of these rifle types and offer some recommendations in a variety of price ranges.