The AR-15 rifle is the Harley-Davidson of firearms—a chassis made to be accessorized. Just as a blinding assortment of aftermarket chrome can be added to Milwaukee iron, Connecticut steel can be tricked out with a bewildering array of grips, stocks, rails, optics, lasers, lights and sights.

With the proper accessories, an AR can be used to see in the dark, punch targets at long range or maneuver in close quarters battle (CQB) confines. More furniture can be hung on an AR than the gun is worth, many times over. The only limitation to accessorizing an AR is your imagination and bank account.

The civilian version of the M4, with its flat-top receiver, is an ideal platform for bedecking a tactical smorgasbord of parts, components and upgrades that fall into several major groups.

Uncle Sam calls the accessories for Special Operations M4s—Special Operations Peculiar Modifications (SOPMOD).

However, even the SOPMOD kit doesn’t include everything. For instance, it makes no provisions for upgraded triggers or pistol grips, and it leaves out sling attachments, assuming the operator will make his own provisions.

Quad-Rail Fore-ends
A quad-rail fore-end is a replacement for the round plastic fore-end that comes on an AR-15. It comes with four sections of MIL-STD 1913 Picatinny rail encircling the barrel from the front sight tower to the delta ring. Some rail fore-ends require work to remove the delta ring (not a trivial task) while others are “drop in.” Rails at 12, 3, 6 and 9 o’clock can be festooned with accessories.

The current SOPMOD rail fore-end is made by Daniel Defense, but also authorized is a Knight’s Armament Co. fore-end known as the RAS (Rail Accessory System). Both are easy to install and leave the barrel free-floating, which is important for accuracy. Regardless of the brand, a quad rail is crucial first step to accessorizing an AR-15.

Optical Sights
Once again, we can start with what’s in the SOPMOD kit and go from there. Special Forces are issued an Elcan 1X or 4X optic. It’s heavy as a brick and about as bulky. However, operators are also given a choice of an EOTech, Trijicon ACOG or an Aimpoint with a 3X magnifier, which most operators seem to prefer over the unwieldy Canadian optic.

Civilians have far more choices. In addition to ACOG, Aimpoint or EOTech, optics include those made by Schmidt & Bender, Burris, Leupold, Weaver, Zeiss and others along with numerous kinds of knock-offs from Israel or China.

Optic Mounts
SOPMOD leaves optic mounts up to the optic provider, but regardless of brand, mounts should be easy to install and rugged. Just be sure to use one that works well for your uses and can handle the punishment that you will put it through.

Back-Up Iron Sights
The SOPMOD back-up iron sight (BUIS) is a round post with an adjustable aperture on top from Knight’s Armament. Very simple, very clean, very unobtrusive. It folds and locks down when not in use, which should be all of the time because a BUIS is just that—a back-up for the main optic.

Some good BUIS are made by Troy Industries, Dueck Defense, Yankee Hill and GG&G. When choosing your BUIS, be sure that they will work with whatever optic is being put on the rifle. These are back-ups, so you may never need them, but they must be easy to transition to in an emergency.

Vertical Foregrip
Vertical grips are all the rage with the M4 because they provide good hand position to work light and laser switches and help with purchase. Some vertical grips, such as SureFire and LaserMax, even come with lasers and lights already attached.

The current SOPMOD in foregrips is the TangoDown quick-detach BattleGrip. This patented design comes with a recessed pocket for either an Insight Technologies or SureFire pressure switch, plus there’s a removable plug to store spare parts, such as an extractor or even extra batteries.

Triggers
One area that is intentionally omitted by the military in the SOPMOD kit is a trigger upgrade. This has to do with user-authorized modifications and armorer-level work, but for most, if you can work a hammer and a drift punch, you can change out an AR trigger.

Since there is no SOPMOD kit trigger, the best way to improve the trigger in an AR is with one of the various drop-in triggers that are available on the market through Timney, Geissele, Wilson Combat or McCormick. All made excellent products that will improve your pull.

Lasers
The current SOPMOD laser (actually it’s a combination laser/illuminator) is the ATPIAL from Insight Technologies, but it is not available to the public.

The one thing that can be said about lasers in general—and this applies to any gun and any laser—is that the more bore off-set you have, the worse your point-of-aim deviation will be. Ideally a laser should be aligned with one axis, preferably the left-right, so that you only have to make adjustments for elevation. Pick one that can do the job at the price you can afford.

White Lights
According to Jim Smith, a Silver Star recipient and former Delta Force operator, a white light is the second most important accessory on an M4 after an optical sight.

The light used in the SOPMOD kit right now is an Insight M3 white light with an IR filter, but previously it was a SureFire MU System WeaponLight. What the SureFire has in ruggedness and durability, the Insight trumps with lightweight and lower cost.

SureFire’s latest M300 and M600 Scout Lights running on LEDs are smaller and lighter than anything the company has made before and, outside of SOPMOD, many operators are fitting them on their M4s left and right.

What’s On Your M4?
The list of accessories for the M4 can go on all night. The comparison to a Harley-Davidson motorcycle is really valid if you’ve got an eye for the Milwaukee iron. Every custom bike is different, even though there are a finite number of accessories. The opportunity to mix-n-match is just endless.

If all this is confusing, Brownells has an excellent feature on its Web site to let you “build your own” AR by clicking on different accessories. This makes tricking out your AR a lot simpler.

For more, check out Customizing an AR Rifle, AR Operating Systems: Gas Impingement vs. Piston, The Specs of MilSpec and The MilSpec Definition.