How to Build an Ultralight AR-15

Ultralight AR-15
Ultralight AR-15

U.S.A.-( The AR-15 has the widest variety of possible configurations of any rifle out there.  From unwieldy “longbow” builds to ultra-short “Han Solo” style single shots, AR builders have long been pushing the platform to extremes.  One direction many have gone is the Ultralight AR-15 route:  there's a 100 page (and counting) thread on where some builders have trimmed their rifles down to 2.5 pounds by dropping every ounce possible and counting each gram.

Ultralight AR-15
My (never-ever) finished rifle stands currently at 4.001 lbs (rifle only) and 4.834 lbs with suppressor and optic.

Not everyone's standards and objectives are precisely the same, as some opt for the lightest build using off-the-shelf parts while others custom trip, snip and shave each part.  The general (unofficial) consensus is that ultralight begins under 4 lbs, while lightweight runs between 4 and 6 lbs.  One thing is certain, the AR-15 platform has been pushed much farther than even Eugene Stoner could have imagined at the time it was created.

My journey with Ultralight AR's began back in mid-2017.  I began researching each part on my own for an article series.  I was quickly directed to the AR-15 Parts Weight Database, a crowd-sourced database showing each part and its advertised weight versus user-confirmed weights.  While the standard is to weigh your rifle sans magazine or suppressor (and to some, optic), my goal was different.  I wanted my rifle, suppressor and optic to come in under 5 pounds.  I was able to achieve that, even improving the weight (or lack thereof) of the rifle a little after the article was published.  My (never-ever) finished rifle stands currently at 4.001 lbs (rifle only) and 4.834 lbs with suppressor and optic.  The wild part is I can easily identify another half pound I could drop from the gun, while still using unmodified factory parts.

So while I'm still a pound and change away from the 2.5 lbs record, here are a few tips I've learned along the way that can help cut the fat from your gun.

1.  Use the parts weight database!

Here's the link.  You're welcome.  All jokes aside, this is easily the best cheat sheet you're going to find on the subject of ultralight AR's.  You can plan out your build with this and save yourself the expense of upgrading to a slightly lighter product down the road when you could have been there at the start.

Ultralight AR-15
The AR15 PWD

2.  High-tech alloys are awesome, at a cost.

With companies like V Seven Weapon Systems, 2A Armament and Fostech (among others) cranking out parts made from magnesium, titanium and lithium-aluminum, unusual alloys have become far more commonplace.  The upside is incredibly strong parts which weigh significantly less than their standard counterparts.  The downside is they usually come at a much steeper price, causing your “dollars per ounce” to skyrocket.  Fostech (receivers) and V7's sister site Dark Hour Defense (forends) both produce the most economical magnesium parts.

Ultralight AR-15
Ultralight AR-15
Ultralight AR-15
2A Armament Lightweight BCG

3.  Polymer to the rescue?

Here's the flip side to point #2: polymer parts are also becoming far more prevalent in use.  I didn't want to use any polymer/plastic in my build (save for the Hogue 15 degree grip and the CAR buttstock), but many have made do with synthetic receivers and even the trigger assembly itself.  New Frontier Armory offers these in a lower parts kit, which at $35 for the pack is a fraction of the cost of the titanium variants.

Carbon fiber is tricky as it doesn't fit in the alloy section up there at #2, nor is it solely a polymer.  It is, however, a very efficient way to purge unnecessary heft.  The Andro Corp carbon fiber buffer tube is 33% lighter than a mil-spec tube.  The Tegra Arms carbon fiber lower receiver is about 5 ounces lighter than most mil-spec receivers.  That's a major difference from just one part.

If you've stayed away from polymer and carbon fiber due to concerns over parts longevity, I'd look into them again.  The gun industry has made great strides in the area of metal-alternatives, with some high round count users having many positive things to say.

4.  The usual suspects

The areas where you can drop the most weight in a hurry?  The Bolt Carrier Group (BCG), receivers, barrels, and forends.  The barrel and forend make the biggest difference in “feel”, as they have the most leverage against the shooter when the rifle is shouldered.  8 ounces near the stock causes less fatigue while shooting than 8 ounces at the end of the barrel.

With barrels in mind, Faxon Firearms' pencil barrels are almost exclusively used for 14.5″ and 16″ ultralight builds.  Their 14.5″ barrel weighs 1.2 lbs or so, with a mil-spec Daniel Defense 14.5″ M4 cut barrel weighing a half-pound more for reference.

Ultralight AR-15
Faxons pencil barrel with Suppressed Armament Systems titanium muzzle brake/suppressor mount

Going from a mil-spec BCG to a DSA low-mass aluminum cuts off right around 7 ounces.  Nearly a half pound, gone.  Side note: reducing the reciprocating mass in the BCG necessitates a change in the gas and/or buffer systems.  It's a subject best covered in more depth that I will here, but know that it's both a necessity and an opportunity to cut more weight if you do it right.  Contrary to popular belief, full-mass BCG's are not an absolute requirement for reliable operation either.

But Why?

The reasons people build light or ultralight AR's are as varied as the shooters themselves.  These builds are often considerably more expensive, so where's the justification?  I've heard many reasons expressed, but here's the most common.

  • American competitiveness.  Taking something good and pushing it to the absolute extreme is a very (though not solely) American ideal.  Look at this screenshot from Wikipedia showing the world's land speed record holders from 1963 to present.  Prior to that, the UK and France dominated the record.  Pushing any mechanical operation to its limits uncovers design limitations that can be improved upon.  The AR platform has undergone many design changes over the last 50+ years, keeping pace with technological advancements.
  • Hunting.  Some who hunt with their ultralight AR-15 plan on cover a lot of ground.  If you have to hike a long ways over rough country, it pays to stay light.
  • Competition.  I've talked with a few professional shooters who didn't have an ultralight AR-15 as their specific goal, rather a byproduct of reducing recoil though reciprocating mass reduction.  Once you start down this path, you find out how incredibly responsive and soft-shooting an ultralight AR-15 can be.

How heavy is your lightest AR?  Hit the comments below.

About Rex NanorumJens Hammer

Rex Nanorum is an Alaskan Expatriate living in Oregon with his wife and kids. Growing up on commercial fishing vessels, he found his next adventure with the 2nd Bn, 75th Ranger Regt. After 5 tours to Afghanistan and Iraq, he adventured about the west coast becoming a commercial fisheries and salvage SCUBA diver, rated helicopter pilot instructor (CFII) and personal trainer, before becoming a gear reviewer and writer.”

-Rex Nanorum


  • 33 thoughts on “How to Build an Ultralight AR-15

    1. Whatever…….
      If you like a light weight rifle fine. I definitely see the advantages and like them. I also like an old school AR for the same reasons I like an M1 Garand. Just something about the heft, the way it feels stable, the sense of durability and ability to withstand heavy use and unintended abuse. I’m not educated on the durability of lighter parts but am impressed with what I’ve seen and heard. It comes down to what you like. How heavy or light it is becomes irrelevant if you cant hit what you’re aiming at.

      1. I love the old M1A, M1 Garand and a handful of other classics. They’ll always have a place in my safe and at my range day. I also have a few more traditional AR’s, but that doesn’t keep me from having a hot rod in there as well. I love them all, as long as they’re accurate and reliable.

    2. Whoa! That’s what I have been calling my 8.5 inch AR-pistol build, Han Solo’s Uncivilized Blaster, finished it three or four years ago. That’s so funny 🙂

      1. Han Solo’s Uncivilized Blaster weighs slightly less than 8 lbs, but that’s with red dot and fully loaded 30 round magazine, by the way..
        Great article, fun to read, thanks!

    3. Built a lightweight for my wife, she loves it. Not super high tech (expensive) but works great and shoots very well. Spinta has great lightweight barrels (w midlength gas tubes) at a good price when you catch them on sale.

        1. Do you have one? Have you you ever had trouble with it or are you just spouting someone else’s opinion? I hate it when someone trash talks a gun they don’t own. Also, bad mouthing someone else’s gun is like someone walking up to you and telling you how ugly your baby is. Shame on you

    4. I like the lightweight concept. I have a “Vietnam” inspired pistol build I love to tote around due to its lightweight. I added a light and a sling no more. Very capable little gun.

    5. if you can’t handle the weight of a standard AR then get your wife to do it for you. Not to be sexist just putting things in perspective for the male ego.

      1. thats some old man misogyny right there. there are dozens of reasons to go light, some he listed some he didnt, your just being derogatory for the sake of being derogatory, get with the times old man

        1. This light-weight contest may be ok for shots and giggles, however. Just think a little deeper. Especially in these times. Think interchangability, adaptability, replacement parts and especially… What do you think happens to your muscle mass, operational and functional memory, as well as your muscle memory when you use sub-standard weights and balances as well as function and accuracy when you have to quickly switch over to standardized versions when your life or the lives of others depends on it but your body can’t quickly adapt to all the variations in a heartbeat when needed to save your life or the lives of others around you? There are many other factors, but this is enough for now.

    6. V Seven / Faxon build at 4 lbs 3 oz. Could shave off another 5 oz by replacing buffer tube and stock with carbon fiber but I like the balance as it is. Rifle is currently aluminum, magnesium, and titanium with no carbon fiber and plastic grip and buffer.

      1. I agree with Gregory…. The thing is, the lightweight ARS go really well with skinny jeans, manginas, tattoos dictated by the “in crowd”, sandals, wannabes and subservient “dudes” who drink warm Starbucks slushies…..

        Then again, I’m 53, still have full use of my gonads and don’t live in my mom’s basement.

        Wood stocks running .308 and I’m good.

        1. I dont think guys with skinny jeans are allowed to own AR’s but no need to be grumpy at guys that enjoy building custom guns. I’m sure you love your off the shelf 308 but I bet my custom 6 pound AR10 308 with 20″ Proof Research barrel can get tighter groups out past a thousand yards even if you wear your favorite overalls

          1. I’m just teasing you guys. Sounds like a nice AR10 (all AR10’s are nice)…
            Not the bib over-all type, but it’d make for a nice day shooting. Once took an old 303 Lee-Enfield with iron sights and cut the legs off a target stand for the guys sighting in their high-end AR’s, scopes -and such- at 600 yards. I was probably just lucky on both shots.

      2. B2, V Seven only makes their handguards out of Magnesium/aluminum not their other parts. They do have a upper, lower and buffer tube made from Lithium/Aluminum. Their 2055 reciever set is just over $700 and it’s not only lighter but also stronger than billet or forget. The Magnesium/aluminum is lighter but much weaker that’s why they don’t use magnesium for their recievers.

    7. My V Seven 2055 build with 16″ Proof Research carbon fiber barrel is 4 pounds 2 ounces but if I downgrade to pencil barrel it’s 3 pounds 12 ounces. No plastic on mine.

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