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How to build a ultra-lightweight AR-15

How to build a ultra-lightweight AR-15

Posted by Daniel Thompson on

As most of us know, the most common questions tossed around in the AR community when building a custom AR-15s are, “How do I build the lightest AR-15 possible?” or “What’s the best lightweight AR-15?” or “Where can I find the lightest AR-15 parts?” or some version of this question.  Who doesn’t want a lightweight weapon that unloaded is less than 5 pounds and can still reach out and touch someone 500 yards away?

I’m going to attempt to answer this loaded question since there are 1000's of different AR-15 parts out there and it’s hard to know which is the lightest or best value for your build, but this will be at least one viable option.

Before we continue, here’s something to consider right off the bat and may stop you in your tracks if you’re looking to build a rifle that can eat mud, be run over by a truck, survive 100ft drops, and never jam.  If those are the most important factors, you should focus your components on them, not weight.  Don’t get me wrong, it’s not that your weapon won't be just fine for everyday use but remember, Rambo wasn’t carrying around a sub 5lb build.  Another thing to consider, if you really want the lightest AR-15 possible then you’re going to pay out the nose for it. There's a huge difference in cost between a lightweight AR-15 build and the lightest AR-15 build possible.

So, here is my attempt at helping you put together an ultra-lightweight AR-15 build with details on how light and how much the different components of the AR-15 build is going to cost.

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LET’S BEGIN!

To start your lightweight AR-15 build off you need to pick up a stripped upper receiver, and a stripped lower receiver.  In the lightweight AR-15 market, there have been major weight savings achieved in specialty alloys and polymers in the last couple of years and those are the categories we’ll be looking at for your ultra-lightweight AR-15.  Aerospace Arms has been in the research and development phase for most of 2016 working on testing some specialty alloys that are substantially lighter than aluminum (about 33% weight savings) and almost as strong.  We aren’t ready to release anything to the public yet because there’s lots of tests that have to be completed before we’ll put our name on it and say with confidence that our products are just as safe as your 7075 aluminum parts.   WE WILL MAKE SURE YOU KNOW WHEN THEY'RE AVAILABLE, but until then, we’ll point you to what currently exists on the market.

THE LOWER RECEIVER

Let’s start with the lower receiver because this one is easy. You don't necessarily need to get a stripped lower because this lightweight item comes as a complete lower receiver. The New Frontier LW-15 is the lightest complete lower on the market coming in at 26.1 ounces. This complete lower receiver is as close to 100% polymer as you can get; everything that can be polymer is (take down pins, hammer, trigger, disconnector, pretty much everything physically possible). The only metal in this complete ultra-lightweight lower receiver are the springs and a few parts in and around the buffer tube. The New Frontier complete lower receiver (to my surprise) is actually really cheap compared to most of the other ultra-lightweight parts we’re going to get into, coming in at approximately $120 before shipping.

THE UPPER RECEIVER

Next is the stripped upper receiver. There are a couple different options and price ranges here that will get you an ultra-lightweight upper receiver. There are 3 main types for options: polymer, lightweight specialty alloy, or milled/skeletonized 7075. The lightest upper I’ve found is the polymer one made by Kaiser US called the KSPUS X-7 coming in at 5.2 ounces, the second is the lithium/aluminum alloy upper receiver made by V Seven Weapon Systems called the 2055 Enlightened AR-15 Upper Receiver coming in at 5.8 ounces, and the third would be some version of the standard 7075 upper that has been milled out or skeletonized to drop weight. A few examples of this are F1 Firearms UDR-15-3G Billet Universal Upper or the Battle Arms BAD556-LW Lightweight Upper. For this build we are going to be using the V Seven Weapon Systems 2055 Enlightened AR-15 Upper Receiver because I am not sure if the KSPUS X-7 upper can be mated to any other lower receiver than the one they offer since they're polymer, which is indicated by the X-7's stripped upper and lower receivers only being sold as a set and not individually.

Now for the price differences between these stripped uppers:

  • The KSPUS X-7 upper is about $125 but since you have to buy the lower and upper together and the total price of the two is $250.
  • The V Seven Weapon Systems 2055 Enlightened AR-15 Upper Receiver comes in at $349 which is crazy high priced when compared to your standard 7075 upper receivers that you can get for around a $100.
  • Lastly are the versions of the 7075 upper milled to remove as much weight as possible. The Battle Arms BAD556-LW Lightweight Upper comes in at $239 and the F1 Firearms UDR-15-3G Billet Universal Upper comes in at $275, which seems about right for each of them considering the work that goes into producing these.

I'm not going to go over all the little parts in this review like the ejection port door, pins for the upper receiver, forward assist, and so on. Both the cost and weight are going to be relatively low compared to everything else in the build.

THE BOLT CARRIER GROUP

So lets move on to the bolt carrier group (BCG) next. The lightest bolt carrier is an aluminum one made by Whiskey Arms coming in at just under 4 ounces.  Since it's so lightweight, you’re going to have to run an adjustable gas block and tune it to the ammo in order for it to function. That is also the weight of the carrier without the bolt in it and the bolt assembly's gonna add another 1 - 1.5 ounces. If your wanting a more all-around lightweight BCG something like the NIB one aim surplus offers for $130 dollars is a good option and weighs about 9 ounces, but there are a lot of different options out there in the 6 - 9 ounce range. The cost for a Whiskey Arms Lightweight Bolt Carrier is approximately $200 dollars but you still have to buy a bolt assembly.

THE LIGHTWEIGHT BARREL

Now you would think at the cost of a Carbon fiber barrel being $500 on up that they would be the lightest out there but surprisingly, you'd be wrong. A Christensen Arms 16" Carbon Fiber Barrel weighs 1.7lbs and costs approximately $500.

Faxon Firearms makes the lightest pencil barrels on the market right now, and they offer two lightweight 16" barrels that will fit our ultra-lightweight build perfectly because they both weight about 1.2lbs! The first option is the Faxon Lightweight 16" 5.56 NATO Mid-Length Pencil Barrel, and the other is the Faxon Lightweight 16" 5.56 NATO Mid-Length SS Pencil Barrel. Either one of them is a great option and will be 8 ounces lighter than the 16" carbon fiber barrel listed.  Looking at the cost, it's a no brainer since the price range for the Faxon barrels is $151 - $161 on Aerospace Arms which is approximately 1/3rd the cost of the carbon fiber barrel.

THE BARREL NUT, GAS TUBE, AND GAS BLOCK

I'm just going to cover these items together and very briefly.  The barrel nut, gas tube, and gas block don't weight much to begin with but if you want the lightest stuff out there, you're going to need a aluminum barrel nut, any gas tube, and a titanium gas block. The total weight from these 3 items should stay right around 2.0 ounces.

NOTE: The handguard you choose is going to determine what barrel nut fits in your build and you might not be about to run the aluminum barrel nut, so be sure to double check this before buying.

THE HANDGUARD

Now with the ultra-lightweight handguards you're going to lose some functionality, well... most all functionality... except somewhere to rest your hand, but like most AR-15 parts, there are a couple different options that are still pretty lightweight and maintain some functionality, but they won't be the lightest option. There are also a ton of different lengths that you can choose from, and of course, the shorter it is, the lighter it's going to be, but we'll stay between 11 - 13 inches for this build.

The best and lightest handguard option for our ultra-lightweight AR-15 build, is a carbon fiber one made by Brigand Arms called the Brigand EDGE.  The 12.3 inch version comes in at only 4.6 ounces (which is amazing), but it's nothing more than a place to put your hand, so don't expect to hang a light off of it. The price may seem a little steep at $329, but it's definitely the ultra-lightweight handguard we're looking for.  

NOTE: The Brigand handguard weight also includes the barrel nut which is 1.4 ounces, so the handguard by itself is actually 3.2 ounces! That's insanely light and perfect for this build.

Now, if you still want something usable but also lightweight, then I would look at the new handguards V Seven Weapon Systems offers. Their new aluminum/lithium handguards are getting pretty close to the weight of the carbon fiber ones but still have a full usable rail. Their 11.1 inch, enlightened, M-LOK handguard weighs only 7.0 ounces and costs $279, so it's a little cheaper, a little more usable, but weighs more than a full carbon fiber handguard.

IN CONCLUSION

Now that we have all the parts and approximate prices, let's add things up and see how much our gun weights, and just as important, how much it cost. Most components are covered minus a couple pins and items in the upper that weigh next to nothing.

Main Parts:                                    Weight(ozs)           Price

New Frontier Lower Receiver            26.1                     $120

V Seven Upper Receiver                    5.8                      $349

Whiskey Arms Bolt carrier                  4.0                      $200

BCM Bolt Assembly                           1.25                     $80

Faxon Pencil 16" Barrel                     19.2                      $161

Brigand Arms Handguard                   4.6                       $329

Small Misc Parts:

Battle Arms Titanium Gas Block         .48                      $80

V Seven Light Ejector Port Door         .29                      $37

V Seven Ultra Light Forward Assist    .32                      $37

          Totals                 63.04 ozs or 3.94lbs              $1427

As you can see, one of the lightest AR-15 you can build is going to cost you about $1500 - $1600 (including shipping costs), but considering that some companies sell their heavy AR's in that range, it's really a competitive price for an ultra-lightweight AR-15 build.  But if that $ amount is too pricey, staying just above 4 pounds can save you a couple hundred dollars if cost is a main concern.

FINAL NOTE

Of course, there are a couple different things you could do to the build to drop even more weight like run a minimalist stock, skeletonize a bunch of stuff, so I don't think it's reasonable to attempt to 100% nail down the lightest AR-15 you can build.  It's your custom build and I hope this article gives you a good idea on how to get started, God bless.

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