If you followed a link to this article or otherwise wound up here, I would direct you to the more recent version of it with updates that can be found here.
In this post, I’m going to discuss what I think is necessary as well as what’s not when setting up a carbine for civilian use. Over the course of my training experiences over the past several years, and with two complete carbines in my safe, I’ve had ample opportunity to play around with various configurations and accessories. I’ve trained with some awesome instructors who have extensive military experience with AR-15 variants, and I’ve taken their advice and opinions into account when setting up my guns. As I continue to learn and gain more experience, and if I modify my carbines further, I will again update this post accordingly.
Some history is in order… for the Defoor Proformance 2 Day Carbine class I took, I elected to use the best upper I had, a BCM Mid-Length with a low profile gas block and extended 12 inch handguard. Mimicking a setup espoused by Larry Vickers and others, I mounted an Aimpoint, Daniel Defense fixed front and rear BUIS (BackUp Iron Sights), with a Surefire X300 Ultra placed ahead of the fixed sight on the 12 o’clock rail. The setup worked awesome in class.
Wanting to free up my X300U to be installed on a handgun, I tried a slightly different configuration of sights and a light on the same upper for a later training opportunity with Mike Pannone. During that class, I used folding BUIS as opposed to fixed and I mounted an old Surefire handheld light in an inexpensive MagPul mount that offset the light at about 1 o’clock. While the setup worked, I should have left well enough alone! The problem wasn’t so much having the light at 1 o’clock, it was more the mount that I chose and how well it worked or rather didn’t work with that particular gun.
After that class, I tried several different light and sight configurations while experimenting with the various different AR accessories that I’ve accumulated over the years. What follows is my rationale for how I have my guns set up, with the caveat that I am a mere civilian who happens to have an intense interest in setting my carbines up for maximum efficiency. For me, the AR-15 is first a home defense weapon, and second a civil defense weapon and natural expression of my interest in firearms. With that said, let me first briefly explain how I have my guns configured right now.
- My aforementioned BCM Recce Mid-Length upper is mated to a Stag Arms lower, and is my “primary” carbine. The carbine has a 14.5 inch barrel with a permanently attached BCM Mod 1 compensator to bring the gun to legal minimum length. A 12 inch Centurion Arms C4 Rail handguard covers a low profile gas block. On the 12 o’clock rail, moving from the receiver forward, I have mounted a Daniel Defense fixed rear iron sight with an XS sight Systems same plane aperture installed, an Aimpoint T1 on a Daniel Defense mount, and a Daniel Defense fixed front sight with a Surefire X300U in front of the sight. This essentially represents my suggested ideal setup. Inside of 200 yards, this is the carbine that I shoot the best. More on this particular carbine and other accessories later.
- My original Stag Arms upper (with a 14.5 inch barrel, carbine length gas system, fixed front sight tower, and pinned AAC flash hider) is now my “backup” carbine. I recently installed a C4 Carbine Length Cutout Rail handguard from Centurion Arms and I have my old Aimpoint CompML2 in a Larue Tactical QD mount on the upper receiver with a Troy rear folding BUIS. This setup allows me to pull off the Aimpoint and replace it with my ACOG TA02, also in a Larue QD mount. I’m not thrilled with the eye relief of the ACOG, since it requires me to almost fully collapse the stock to achieve the correct eye relief, but this configuration does allow me to keep a rear BUIS and switch between the RDS and magnified optic as needed. Since this carbine is still my suppressor host for right now, I wanted the ability to use either my Aimpoint or my ACOG as circumstances dictate. Fortunately, the Larue Tactical QD mounts that I use with my optics are capable of a repeatable zero despite removal and replacement. I also am trying out a new Streamlight ProTac Rail Mount 1L. After much experimentation, I currently have the light mounted in a Larue Tactical offset mount on the 3 o’clock rail with the light in the 1 o’clock position. With the fixed front sight base and pinned muzzle device precluding a 12 o’clock light mount, I think having the light at 1 o’clock alongside the front sight tower is a good compromise. Again, more on this later.
With that long-winded background explanation out of the way, let’s talk about how to set up YOUR carbine. As with much on this blog, this is primarily directed at civilians, rather than military or police that may have different objectives and requirements. Whatever configuration and accessories you choose for your carbine, I urge you to vet it in training to find out what works and what doesn’t. Here are my thoughts on the subject.
Mil-Spec
This term is bandied about a lot, but what does it really mean? I think it’s a good starting point, but it’s not the end all be all. The reason that my backup carbine is a backup is because I initially wanted and thought I needed a mil-spec AR-15 when I started my AR-15 journey… remember that mil-spec is closely tied to lowest bidder! That’s not necessarily a bad thing, but nor is it necessarily a good thing. Choose wisely, and remember that you often get what you pay for.
Barrel Length, Gas Systems, and Twist Rate
For a civilian defense carbine, I think either a 16 inch or 14.5 inch barrel with a pinned muzzle device is the best compromise. You can certainly go shorter if you venture into NFA territory with a SBR, or you can get an 18-20 inch barrel (but that would be a rifle instead of a carbine). I have gravitated towards 14.5 inch barrels with pinned muzzle devices to bring them to minimum legal length for my guns (keep in mind that I am short and of small stature). Many will no doubt advocate for a 16 inch barrel to avoid a pinned muzzle device, and I do not disagree with that premise. I just happen to prefer mine short, just like my women!
When I ordered my Stag Arms LE/SBR 14.5 inch upper, I did so specifically because Stag Arms didn’t offer a mid-length gas system. Indeed, if I were going to buy a 16 inch barrel, I would select a manufacturer that offered a mid-length gas system. This is because of the underlying design of the direct impingement system employed in the AR-15. If you compare the rifle length gas system on a 20 inch barrel, a mid-length gas system on a 16 inch barrel, and a carbine length gas system on a 14.5 inch barrel, you will note that the distance between the gas port and the muzzle on all three are approximately equal at 7 inches. There is a reason for this. Moving away from the original design represents a compromise to achieve different design parameters. This is one reason that short barreled ARs have a reputation for being finicky. The AR was originally designed around the rifle length gas system. Subsequent design compromises have been necessary to make the shorter gas systems run reliably. Having said that, one recent innovation by manufacturers is to utilize longer gas systems on shorter barrels. As opposed to using a carbine length gas system with 16 inch barrels, the current trend of 14.5 inch mid-length or 18 inch rifle length uppers yields a softer shooting weapon with less wear and tear on components. Indeed, my BCM 14.5 inch mid-length upper is the softest shooting carbine that I own. With appropriate ammunition and spring and buffer combinations, it runs like a Swiss watch!
Common twist rates for ARs are 1/7, 1/8, and 1/9. It probably doesn’t matter too much which you choose unless you are planning to shoot either very light or very heavy bullets. All of mine are 1/7 in order to be able to handle the heaviest bullet weights while still offering adequate performance with the common 55 grain FMJ.
Caliber is a whole ‘nother can of worms, but the short answer is that you can safely shoot .223 ammunition in a carbine chambered for 5.56. The opposite is not necessarily true. For that reason, I suggest choosing a barrel chambered for 5.56.
Sights & Optics
I took my first carbine class with Paul Howe at CSAT using iron sights. While I think it was an invaluable experience, I also think that optics are ubiquitous for good reason today.
Whether you choose a non-magnified red dot sight or a magnified optic is going to be largely based on your intended usage. I think most urban dwelling civilian carbine owners using the carbine for defensive purposes in and around their homes are going to be best served with a red dot sight. I’m going to further specifically suggest an Aimpoint sight. This suggestion is predicated on rugged durability and remarkable battery life. Leave the sight on all the time and change the battery annually on a specific anniversary or holiday.
While EOTechs have versatile reticles, they suffer from poor battery life and other issues. Yes, SOCOM used them, but I also have it on good authority that SOCOM changed batteries on a DAILY basis when operational. I don’t know about you, but I can’t and won’t budget for that many batteries!
I am of the firm opinion that with non-magnified red dot sights, back up iron sights are mandatory on a fighting rifle. I don’t really think it matters whether you run fixed or folding BUIS with a RDS, but there are a couple of advantages to the way I have my primary carbine set up. Specifically, in case of battery or dot failure, the backup sights are already there if needed immediately. While some may find the sight picture with fixed sights in the field of view too “busy”, with a lower 1/3 co-witness it doesn’t bother me. I can say this with confidence having used the exact setup in more than one class.
(In case I just spoke a foreign language to new gun owners, lower 1/3 co-witness means that the iron sights are visible in the lower third of the red dot field of view during normal use. If you were to lower your eye so that the dot also appeared to be in the lower third of the field of view, you would note that the irons and red dot coincide.)
Continuing briefly on the topic of iron sights, I have same plane rear sight apertures on both of my guns. This simply means that if I switch between the small or large aperture of the sight, there is no shift in my point of impact. The original M16 iron sights were designed with long range and close range apertures. Flipping between the two apertures resulted in a change in point of impact that was supposed to account for bullet trajectory. A few schemes have been developed over the years to deal with the elevation turret that was later added to the rear sight, but considering typical carbine engagement ranges outside of the military context, I think a same plane aperture sight is a better idea. XS sights makes a nice same plane aperture sight that even has one aperture offset slightly to account for the shift in windage when the aperture rotates on the adjustment screw. Flip to the large aperture for close range engagements and use the small aperture to zero and for longer range targets. Another good option is the CSAT rear sight aperture also offered by XS that was designed by Paul Howe. You can read more about that option here.
While I don’t have a lot of direct experience with magnified optics on ARs, I will say that if I were going to do it all over again, I would probably choose a 1-4x or other similar low power variable optic with an illuminated reticle instead of the ACOG that I have now. The ACOG is bombproof, but suffers from poor eye relief and the fixed magnification is not necessarily ideal for the close quarter environments in which civilian owners would most likely employ a carbine. Rather, I envision my ACOG equipped carbine as more of a general purpose rifle for outdoor use. Having said that, with the ACOG’s LED illuminated reticle, in close quarters the Binden Aiming Concept works well, similar to the original Occluded Eye Gunsight used by the Son Tay Raiders.
As a further point of discussion, I’m no longer convinced that BUIS are absolutely necessary with modern scopes that do not depend on batteries to function. In other words, with illuminated scopes, the etched reticle is still perfectly usable in case of battery or electronics failure. Some notable instructors no longer even use BUIS on their rifles. John “Shrek” McPhee and Frank Proctor are two that I know of. Grant Cunningham has also weighed in on the subject and I find his line of reasoning to be similar to mine. That is, BUIS are only really needed when your primary sight is dependent on batteries or electronics to create a dot or reticle.
Lights
Since well over half of our lives are spent in darkness (or indoors), and since carbines generally require two hands to operate, I think a weapon mounted light is necessary on a carbine intended for fighting. When choosing a weapon mounted light, I think the 12 o’clock mounting location offers some distinct advantages. First, the location offers easy ambidextrous access. (With a Surefire X300U specifically, the switch activation is identical no matter which hand is used.) Second, any barrel shadow in the beam pattern will be where it is least noticeable and least critical, namely below your line of vision. Finally, having the light body at 12 o’clock positions the light in an ideal position to be used with cover or barricades to either side with the light in line with the sighting system. Even if you have to cant your weapon to fit through an opening, if you can visualize the target, the light will fit! There are several options when choosing a 12 o’clock mounted light depending on your budget and preferences, and I even know of one aftermarket front sight that integrates a light mount into its design.
If for whatever reason a 12 o’clock light mount won’t work on your carbine (my backup carbine with its fixed front sight tower and carbine length rail is one example), then I think an 11 or 1 o’clock position is the next best option. In continuing this paragraph, keep in mind that I am but a lowly civilian and NOT a door kicker. As noted above, I have settled on using the new Streamlight ProTac Rail Mount 1L light in a Larue Tactical offset mount for my backup carbine. I have it mounted forward on the right side rail in the 1 o’clock position. With the light positioned this way, the tail cap switch is easily accessed with my support hand thumb by reaching over the top of the rail and I can also easily reach the switch with my right hand thumb if I transition the rifle to my left shoulder. I think this maintains many of the advantages of the 12 o’clock position, although splash back from barriers is a minor concern when shooting around the left of cover. In truth, I have the light mounted on the 3 o’clock rail because the mount’s throw lever interferes with my normal grip with the light mounted on the 9 o’clock rail. Having said that, I would prefer the light in the 11 o’clock position versus the 1 o’clock position that I’m using. The reason for this is the only time I can really think of that I would move the rifle to my support side shoulder (as a right handed/right eye dominant shooter) is to fire from behind the left side of a barricade or cover. In that instance, splash back of light from the cover would not be an issue with the light at 11 o’clock. Conversely, the way I have it now, I don’t have to worry about splash back when shooting from behind the right side of cover or a barricade. Everything involves a trade-off… which brings us full circle around the clock and back to the 12 o’clock light position!
For those of you that have M-Lok or KeyMod rails that are considering an offset mounting position, Way Of The Gun (Frank Proctor) has just released a new Scout pattern light mount that is extremely low profile and inexpensive as well!
I have also played around with the ProTac’s included remote switch option on the 12 o’clock rail, but I maintain some concerns about durability, inadvertent activation, and increased complexity that lead me to generally eschew tape switches.
I do know that a few trainers suggest a 6 o’clock mounted light for good reasons, but with my guns and lights, I definitely prefer the light mounted above the axis of the bore, primarily to keep the thumb activated switching consistent among my long guns. On my backup carbine specifically, I found the rail available behind the fixed front sight base too short to comfortably accommodate a 6 o’clock mount. Also, with the light mounted so far behind the muzzle, the barrel shadow was considerable.
Finally, I should note that my frustration with finding a good light mounting option for my backup carbine is what led me to strongly prefer an extended handguard covering a low profile gas block!
Slings
I’ve heard the comparison that slings are to long guns as holsters are to handguns, and I agree. If you have to use your hands for other tasks or if you must transition to a pistol, a sling is an invaluable and essential accessory. For a variety of reasons, I think having a quick adjust two point sling is ideal. I have a Blue Force Gear VCAS with sewn in QD swivels on each of my carbines, and the slings have worked well for me. The Viking Tactics sling or Sheriff of Baghdad B-Sling are other good choices.
In the past, I chose to mount the rear of the sling to the opposite rear of the stock to hold the carbine in tight to the body when slung and to facilitate easier shoulder transitions. However, I now choose to mount the rear of the sling to the rear of the receiver near the castle nut as advocated by Defoor. Having run essentially the same carbine both ways (sling attached to stock and sling attached to receiver), I can say with certainty that I prefer the latter for easier carbine manipulations. Both methods work, but with multiple QD mounting points on the carbine, I can easily change my setup as dictated by situation or preference.
One further note regarding slings… for storage and use in vehicles, it is strongly advised to fold the sling in on itself and band it to the collapsed stock in such a way that it will be deployed either when the stock is extended or by pulling it out as needed. Sheriff of Baghdad Combat Bands work well for this purpose, as does a short piece of inner tube. The BCMGUNFIGHTER Stock is specifically designed for this… and that is the stock that I will probably purchase if I ever need or want a different one.
Triggers
There is nothing wrong with the stock AR-15 trigger. Having said that, many shooters prefer an aftermarket trigger for enhanced performance. I personally like the ALG Defense ACT trigger. It offers mil-spec reliability, is an excellent value for the price point, and offers enhanced performance over the stock AR trigger. I also have an ALG Defense QMS trigger in my backup gun, and it is a definite improvement over the stock trigger. I would caution against excessively light or adjustable triggers intended for competition being used in a carbine intended for self-defense. I personally want my trigger to be dead nuts reliable when I need the gun to go bang!
Handguards
There are a plethora of aftermarket handguards available from a multitude of manufacturers these days. As should be obvious by now, I am a fan of the rails offered by Centurion Arms. Whether you choose a slick, a Picatinny quad, a KeyMod, or an M-LOK handguard, I think that light weight and extended length are paramount. The extended length allows you to place your forward hand wherever it is comfortable and convenient, allows you to easily configure your lights and sights to work together, and makes shooting around cover while using that cover as a rest easier. For me, 12 inches is a comfortable medium. While drop-in handguards are easy to install, I prefer handguards that free float the barrel.
As far as rail mounted accessories are concerned, I think sights and lights are appropriate. I don’t really care for vertical fore grips, as they essentially lock my hand into one spot on the handguard even though different positions and scenarios may require different hand placements. Every time I’ve tried running a VFG on my carbine in training, I’ve wound up removing it in favor of running the carbine slick. As with everything, YMMV! Obviously, multiple lights and lasers mounted on the rail may confound the issue of hand placement. If a VFG is used, then I think it is probably best placed far forward on the handguard so that the proper hand placement for the kneeling and prone positions can be maintained. This is yet one more reason that I like extended free float rails.
Lower Receiver Furniture
I like the MagPul CTR stock myself… it does everything I need it to with aplomb. There are once again many good options to choose from, and having an adjustable stock is a good thing. I personally run mine one click in for an ideal length of pull for my stature.
Similarly, there are several aftermarket grips available, choose one that fits your hand. I like the MagPul MOE-K2 version for consistency among my guns. The steeper grip angle of the MOE-K2 works well for my AR pistol and is comfortable on all my ARs, so I just run the same grip on all of them.
Other Accessories
The only other accessories that I universally install on any carbine are a BCM Gunfighter Mod 5 (small latch) charging handle and a MagPul Enhanced trigger guard. That’s it.
Discussing all of the accessories available for the AR-15 in today’s marketplace would result in an endless article. Instead, I want to say a few brief words about what you don’t necessarily need! I am not a fan of ambidextrous controls or other bolt release enhancements. The only possible exception that I haven’t yet evaluated but that I think makes sense is the Redi-Catch offering from Redi-Mag that allows the bolt hold open to be actuated with the magazine release. It appears simple to install with minimal impact on weapon handling. As far as ambidextrous controls are concerned, I’ve learned how to perform left handed carbine manipulations, and the specific procedures are simple and effective. I just don’t see the point in unnecessarily complicating a standardized simple and reliable system. Furthermore, with more than one carbine in the safe, adding the same accessories to each carbine for the sake of consistency gets expensive fast! The exception to the above advice is that there are now new AR-15 designs that come from the factory with fully ambidextrous controls. I’m just not a fan of retrofitting older guns or traditional designs to try and accomplish the same thing I can do with simple manipulations that cost me nothing.
So there you have it. My thoughts on setting up a carbine for self or home defense, worth exactly what you paid for them!
As always, we welcome your comments, questions, and critiques of our writing and ideas here at the blog!
CIVILIAN GUNFIGHTER 
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