The Best Lightweight AR-15 Build

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Recently, I filed a Form 1 with the ATF to turn my 11.5-inch Geissele Super Duty pistol into a SBR, as it is one of my favorite ARs, and I wanted to outfit it to its full potential. Complete with a SureFire Scout Light and RC2 suppressor, SIG ROMEO8T optic, Griffin Armament backup irons, and B5 Systems Bravo stock, I had a hardcore daylight setup suitable for SOCOM. When I was done, I was shocked at the weight — my suppressed SBR weighed 9 pounds, 4 ounces empty. This is completely ridiculous. A short-barreled 5.56 that weighs as much as an M1 Garand before you even add ammo? Come on.

I recently built up an 11.5-inch Colt 733 clone (the rifle Robert DeNiro and Val Kilmer both run during the bank robbery scene in “Heat”), and that retro gun only weighs 5 pounds, 6 ounces. Now, admittedly, that 11.5-inch SBR didn’t have a light, an optic, or a suppressor, but somewhere, there must be a happy medium between weight and features. So, I went to work on the Geissele.

In gradually paring down the weight of my AR, I realized that it is easy to shave significant weight off your gun without affecting performance or looks. Whether you’re looking to lighten an existing AR or planning a build, considering the weight of various components in advance can make a significant difference in the overall weight of the finished product. Ounces add up to pounds quickly.

Why Build a Lightweight Rifle?

For those building up a gun, the barrel is the single heaviest part in an AR-15, and unless you’re constructing a DMR-type rifle for regular use at extended ranges, you don’t need a heavy barrel. Heavier barrels aren’t inherently more accurate; they just resist heat-related zero shifts longer. Most lightweight or “government profile” barrels from commercial manufacturers will achieve 1 to 2 MOA with ammo they like, which is all you need, especially if you’re just running a red dot. The weight difference between a 16-inch lightweight barrel and a 16-inch SPR/H-BAR barrel is a full 11 ounces, and that difference is right where you’ll notice it most.

If you’re building a gun or considering swapping out your rail, there are dozens if not hundreds of quality options on the market. Most rails today use proprietary barrel nuts, and sometimes there’s as much weight variation in those as there is in the rails themselves. So, when comparison shopping, don’t just look at the weight of the rail but also that of all the mounting hardware.

Unless you’re planning on airborne assaults, any rail is likely strong enough for your needs. To prove that, I’d like to point to the U.S. Border Patrol’s solicitation for their new patrol rifles. The specifications only listed weight — not strength, a maximum 9.5 ounces for a 15-inch rail (not including mounting hardware), which is darn light. So, choose a rail that provides the features and looks you want without adding unnecessary weight. Geissele won that contract, and their 14.5-inch carbine with its government profile barrel weighs just 6 pounds, 1 ounce.

Thin/light rails heat up quicker, but if you’re worried about that, consider investing in some rail covers, which work and don’t add much weight. The first ultralight rails I ever tested were from SLR Rifleworks, and their 15-inch Ultra Lite rail, with mounting hardware, weighs just 10.7 ounces.

My current favorite “light” rails are the MCMR rails from Bravo Company. For comparison, the 15-inch Bravo Company MCMR rail with mounting hardware weighs 11.5 ounces. The 15-inch version of Geissele’s slim MK16 rail weighs 17.1 ounces with all the hardware, because it’s ultra-beefy around the proprietary barrel nut. You can easily shed some significant weight with your choice of rail, so be sure to do some comparison shopping.

Something else that will take your hand away from the heat of a skinny rail is a vertical/angled grip or hand stop. And on that note, you can’t save significant weight everywhere. There might be an ounce or 2 difference between the various handstops/short vertical foregrips and weaponlights (SureFire, Streamlight, Modlite, etc.), but that’s about it. You’re better off choosing whichever one works best for you. There’s no practical difference in weight between the various pistol grips on the market.

Heavy Cans

Everybody is adding suppressors to their guns these days, but a suppressor is a significant chunk of weight right at the muzzle where you’ll notice it most.

The suppressor on my SBR when I noticed my weight “problem” was the SureFire SOCOM556-RC2 mounted on their quick-attach SF3P flash hider. QD suppressor mounts are cool and convenient; they allow you to swap your can between various guns quickly and easily, but they always add weight and sometimes length compared to direct threading. That SureFire SF3P flash hider alone weighs 3.9 ounces! Add the combat-proven 17-ounce RC2 with its all-Inconel construction built tough enough for sustained full-auto fire, and it completely changes the balance and feel of your gun — and not in a good way.

For testing, I put the new Banish Speed K from Silencer Central on my Geissele. This is a direct-thread can that helps keep the weight down, and it’s short, which helps keep the balance point back as far as possible. It’s 14.1 ounces, which is not light, and you still notice that weight, but that’s still nearly a 7-ounce savings over the SureFire setup.

Weight is the reason most suppressor manufacturers offer titanium versions of their cans. While more expensive, titanium cuts the weight nearly in half, usually only affecting performance a bit. Silencer Central makes a titanium version of the Speed K that only weighs 8.6 ounces, which is a huge additional weight loss. The Inconel construction of traditional suppressors mean they’re tougher, sometimes full-auto rated, but a titanium suppressor should still handle as much abuse as your rifle can take/give out and won’t wear out before your barrel does.

Depending on what kind of AR you’re building up and your specific needs, your choice in optic might not be much of a choice at all. While I love the performance and versatility of LPVOs, every time I think about putting one on an AR, it’s the weight of it that gives me pause. Between scope and mount, you’re talking about adding at least 1.5 pounds, probably more like 2 — the higher the magnification, the higher the weight. QD scope mounts, just like QD suppressor mounts, add more weight. You’re likely going to choose your scope based on performance rather than weight, but don’t ignore the weight, or you might regret it, and in today’s market, you have plenty of options. Personally, I’m a big fan of both the Nightforce NX8 1-8X and Primary Arms’ PLxC 1-8X as they are both compact and, at 17 ounces, about as light as you can hope for in a 1-8X scope.

Optic Selection

I’m also a fan of Trijicon’s TR24 AccuPoint scope, specifically with the fiber-optic-illuminated triangle reticle, which can be run like a red dot at 1X. Sure, it’s “only” a 1-4X, but that lower magnification range means not just a lower cost but a lighter scope. In this case, it’s 14.4 ounces. The TR24 is my “end of the world” LPVO. I once owned the famous ELCAN Specter DR 1-4X switchpower scope and, like most everyone I know who had one, ended up selling it as it was so darn heavy (23 ounces).

If you’re considering a red dot, there are significant differences in size and weight. The EOTECH HWS is a perennial favorite, but it is not especially light at 11.2 ounces, though that weight does include the mount.

I like the SIG Sauer ROMEO8T optic, which is like an EOTECH HWS on steroids. That’s what I initially had on my Geissele. It has the same large window and circle/dot reticle as the EOTECH, with a built-in mount, flip-up lens covers, and incredible battery life (100,000 hours). However, it weighs 13.7 ounces. Nearly a full pound for a non-magnified red dot just doesn’t seem like a good decision.

I swapped out the SIG for Aimpoint’s new Acro C-2. The C-2 is intended for carbine use. It has a smaller 2.5-MOA dot and the same 50,000-hour battery life, but it comes complete with flip-up lens covers and a flat-top AR mount. You have your choice of a Reptilia Corp, B&T, or Scalarworks mount. I chose the Reptilia, and the optic complete with mount and lens covers weighs just 4.3 ounces.

Final Weigh-In

Whether you’re adding a brace or a stock on the back of your AR, there is a huge difference in weight between many popular offerings on the market. Mission First Tactical’s BATTLELINK Minimalist stock might still be the lightest AR stock on the market at 5.8 ounces (not including the buffer tube), which is why it’s so popular. Compare that with Magpul’s UBR Gen2 stock which, even lightened up by 20 percent over the original, weighs 18.8 ounces.

On my Geissele SBR, I initially mounted the Bravo stock from B5 Systems. I liked the look of it … but the Magpul MOE SL-M only weighs 7.1 ounces, and is just as functional and good-looking.

So, for my personal diet plan, simply by swapping out my SureFire SOCOM556-RC2 for the Silencer Central Banish Speed K, the SIG ROMEO8T for the Aimpoint ACRO C-2, and the B5 Bravo stock for the Magpul MOE SL-M, I took 18.4 ounces of weight off my SBR and shortened it by almost 3 inches without negatively affecting performance or looks. At some point, I’ll be getting a titanium can for this build, which will shave another 4 to 6 ounces off the front of the gun where I’ll notice it most.

Chances are, if you’ve got an unreasonably heavy AR on hand, you can shave serious weight off it as well simply by swapping out a few pieces as I did. If you’re building up an AR with a barrel length of 16 inches or less and are concerned with weight, there’s no reason why you can’t keep the empty weight of that gun (minus optics and accessories) at or under 6.5 pounds and still have it be fully featured.

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