Ultralight Ar15 build

I recently came across a few articles on alloutdoor that refer in some way to ultralight ar15 style rifles. I did some internet snooping and found a few builds, and the Bentwood OIP. This rekindled an interest of mine, the sub 4lb ar15. I am not wholly new to UL ar style rifles, I have an original, pre bushmaster, Professional Ordnance Carbon 15 rifle, and one of my pistol builds has a PO complete upper (uses a std ar15 bolt carrier, with the PO propitiatory bolt).

This reading got me interested so I started looking at the parts in the OIP, found V7 systems and all of their titanium parts (ohhhhhhh).

I have a "semi" lightweight build, 14.5" carbine pencil barrel on a matched spikes receiver set with a samson 9" evo rail. It is reasonably light and points well, but the FH that is welded on the barrel to get it to legal length is heavy. So I started to look around for lightweight parts to do a scratch build.

First thing I found is that light parts are expensive, and I would need an adjustable gas system, since I planned to use a low mass bcg and buffer setup. I priced all of the titanium and 7075 al small parts. The lofty price tags got me thinking: Can I use cheaper alternatives and lighten them myself? I have a mill and a lathe, plus a bunch of other tools and a small amount of skill! I figured I could give it a shot.

This build will likely yield 2 rifles, as I have sourced parts and ended up with multiples of the same. Plus it will give me the opportunity to try different approaches with my material removal techniques, as well as allow for comparisons.

Feel free to follow along, I will post pics and info. My main goal here is to end up with a sub 4lb rifle with the optics. Secondary goal is to use as many metal parts as possible, and third is to keep the cost down as low as I can. I will be using as many off the shelf parts as possible, and will limit my work to modding existing parts, rather than building items from scratch.

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My research has revealed that the heaviest components of the rifle are the best place to start, not surprising here. The receiver pair, barrel, bcg, and furniture generally are the heaviest components.

I have a 14.5 pencil profile carbine barrel in my spares, not sure of the brand as I had the gas block journal shortened to match a low profile block a few years ago by a machinist buddy and the info was milled off. This was before I had a lathe.

I recently purchased a Faxon pencil 14.5 from aim surplus on sale for 160 shipped. Faxon appears to have the lightest barrel, and I plan to copy the profile on the 14.5 barrel I already have. I will post weights soon, but the Faxon is a few ounces lighter than my other barrel. Downsides are few, the midlength gas port being the major issue as it will require a longer hand guard to cover compared to the carbine barrel.

Did measurements, and a 9" rail will work on the carbine, and a 10" should be ok on the midlength. Started searching for a suitable rail and ended up with 2 choices. BCM used to make a magnesium alloy hand guard, the KMR. V7 Systmes makes a titanium barrel nut and clamps which are about half the weight of the BCM parts. Hover this was getting pricey, almost 300 bucks. Other option is to go with a carbon fiber tube, but again the price is high. I started looking for alternatives, and found Chinese knock offs of the Noveske NSR. I have a 7" NSR on my 7.5" barrel pistol build. Turns out you can get the Chinese copy with an aluminum barrel nut. I figured I could get the 9" down to around 6oz with barrel nut with some milling on the pict rail section and still have the versatility of the keymod. And the price is around 35 bucks. So I ordered a 9" and a 10", however the 10" has to come from china so it will be a few weeks. I have the 9", and have already done some milling on it. I will add weights, before and after, along with pics later.

Now will be a good time to discuss the intended use of these rifles. They are not meant to be "go to war" tools. I would view them as pack guns, possibly backup or bug out items. I would not task them in high fire volume situations. I plan to run red dots for weight savings so they will not be long range guns either. I will consider them as defensive tools in a minimalist carry situation, and also good as loaners for smaller stature/weaker shooters. Just a little POU there, i think it is important to have a semi defined use.

Barrel and rail covered, I moved to receivers.

2a Armament and Battle arms development both sell nice, light, matched receiver sets. Both are over 500 bucks.

I have a EP Armory poly lower that I machined a while back. While I do not really want a poly lower, I am interested to see how it compares, so I will throw it into the mix. I need to take all of the LPK parts out so I can weigh it.

I also have a cast 80 percent lower, which I plan to machine. I will also mill the outside to save weight, not sure if I will go to a full skeletonized cut. Looking at the BAD and 2a lowers, they have removed weight by adjusting the external contours, so I will do the same.

I am a fan of the Anderson "slick side" uppers, and have a few spares on hand. I do not see a need for a forward assist or port door. The Anderson does have a shell deflector, which I plan to skeletonize. I will also remove most of the pict rail on top, leaving enough to mount the red dot at the front of the upper. beveling the edges and some milling will lighten the upper some more. I am sure I can get it to the same weight as the expensive alternatives listed above. Both guns will use this receiver, as it is the cheapest metal alternative I can find at 40 bucks.

While looking for a lightweight BCG I investigated many options. JP, BAD, and quite a few others make steel, lightened, BCGs, however they are pricey. I am staying away from the titanium and aluminum carriers, as they are cost prohibitive, and i would like to see how I do with steel parts. Aim Surplus has a house brand lightweight BCG, and it was on sale for 90 bucks so I picked one up. A std BCG clocks in around 11 ounces, and the AIM BCG is 8.9 ounces. Buffer searches ended with TAC CON and their 1 ounce, 2 piece buffer. Not sure which spring to use, but the Tubb flat wire is my main choice right now.

Adjustable gas systems have taken a fair amount of time to research. I ordered a superlative arms, bleed off style gas block, but then found rubber city armory's adjustable gas key, which I did not know even existed so I ordered a few to try. More info when I get them in hand.

About 2 weeks ago I started searching for a light grip option for the lower. Magpul K grip is the lightest, has the benefit of having a steeper angle than an A2. However it fells too small in my hand. Going to the K2 grip adds alot of weight. The B5 grip is lighter, so i got one of those and started forming a plan to lighten it.

I did a test run on an A2 grip. I sanded the entire outside down, basically removed the texturing and a little more. Still felt solid. So I cut the bottom portion off, to fit my hand and end just below my pinky. I also drilled some holes in the top, near where the safety spring goes. Cant see them when installed, lost some more weight. However the angle is just too steep, feel very weird with the short stock (more on that later). A shame cause I got it down to around 1 ounce.

I did the same mods to the B5 grip, not done yet but I will post pics and weights of the process when complete. All of this work saves an ounce, or slightly more. Not sure if I can get it down to as light as I got the A2, but I will try!!! I ddi buy a ti grip screw for 5 bucks form V7 when I order the Ti brake,

I did some math with the V7 parts info from their site. What it boils down to: you can expect to spend around 6 to 7 dollars to save a gram when going to the lightweight titanium/aluminum parts. and with 28 grams to the ounce, cost adds up fast. If I can remove one ounce of weight from the grip, that saves me from spending about 200 bucks on lightweight parts. Those parts would be the takedown pins in 7075 al, mag catch assembly in 7075, hybrid al/ti selector switch, ti firing pin (which I may still do as I have found them for 13 bucks), and a few other small parts. I really cant see spending 200 bucks on 1 ounce, since the lw bcg saved me over 2 ounces and was not any more expensive than a std bcg. If I was going for a record I might spend the money, but I am not... so cost cutting is the order of the day!!!

I have been considering something like this recently, had a list for parts to make an 11.5" pistol for a hair over 5lbs with spikes aluminum folding sights.

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I came to suggest the taccom buffer and RCA adjustable gas key. Glad you found those, they have worked well for me. With that system you go to a regular low-profile aluminum gas block (also cheaper).
I went with a carbon fiber handguard from dpms that was super cheap, $60ish. You had to epoxy it to the barrel nut though. I think Clark Custom makes a similar product.
I found these guys after and wished I had knowed about them, good price on a lightened lower: http://www.vorn-usa.com/product-p/vl2.htm
New frontier armory has polymer trigger parts. I tried one a while back and the trigger pull is a lot better than I expected.

Good info guys, many thanks! I will look into the cf hg from dpms.

I may go with a titanium gas block, but the aluminum models are much cheaper... I plan to try the superlative gas bleed setup just to see if it is any better than the gas key.... I doubt there will be much difference.

jdindadell said:

Good info guys, many thanks! I will look into the cf hg from dpms.

I may go with a titanium gas block, but the aluminum models are much cheaper... I plan to try the superlative gas bleed setup just to see if it is any better than the gas key.... I doubt there will be much difference.

Click to expand...

What's the supposed advantage to this "gas-bleed" setup vs other gas blocks?

If you are going to do a pin and weld look into the VooDoo manimal flash hider. It's .750 diameter extended A2 type and is very light, designed for users to be able to remove gas blocks and barrel nuts with a pin and weld. Faxon has a couple options in the area as well they just released. They are also much cheaper than a titanium alternative.

You could also take a standard FGC and bob the hammer to shave some weight off with the added bonus of reducing lock-time.


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I have a friend that built two (non-SBR's) with as many titanium parts as possible. It is very expensive and hard to source the parts. I think they are 4 pounds even. They feel like air soft toys.

Buffer recommendation: remove the weights from a standard buffer, cheap and light. Also reduced power springs work well with lightweight BCG and adjustable gas, you can get them from wolf or TTI. I have an extra that I would be more than happy to donate to your project.

Titanium is overrated IMO. Cost to weight savings is stupid money to me. The only thing I could see being replace with titanium is the takedown pins. Castle nut and end plate can both be had in aluminum, safety switch can be replaced with partial plastic parts. I would not remove the weight from the buffer as the reciprocating mass is needed for when the bolt closes to prevent bolt bounce. Reduce it, sure but not remove it.

Also reduced weight buffer springs may have an adverse effect on reliability when the rifle is dirty, inhibiting it from fully feeding fresh rounds from the magazine. It will probably take some trial and error.


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a little late but did you look at the Clark CF freefloat tube?

I have a mid weight M4 set up that I'd like lighter. Pencil barrel, lighter nut, etc.... I've been toying with this for a while.

DaSouthernYankee said:

I would not remove the weight from the buffer as the reciprocating mass is needed for when the bolt closes to prevent bolt bounce. Reduce it, sure but not remove it.

Also reduced weight buffer springs may have an adverse effect on reliability when the rifle is dirty, inhibiting it from fully feeding fresh rounds from the magazine. It will probably take some trial and error.


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Click to expand...

Weighted buffers are not needed in systems where you can control the gas. His project is focused on weight, it will be extremely reliable as long as the gas is adjusted properly. Over gassed systems need extra weight and strong springs, but that's not what he's building.

Just found another part to save some weight. Fostech has apparently revived the magnesium receivers that mag tactical had before they went under. Supposedly they are 35% lighter than a standard lower and can be had for well under $100. The rear where the buffer tube threads in has also been reinforced to prevent failures known with the old mag tactical lowers.


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Fits had some mag tactical magnesium lowers $75

As of how long ago?


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2-3 weeks ago. They had about a dozen.

Lots of response, woohhhooo! I always enjoy a thread when a lot of people jump in!

I saw the magnesium lowers, those look interesting and I would like to try one.

I went with a 1 ounce, 2 piece buffer system from Taccon. We shall see how it does.

I am actually building 2 of these, as I have a pencil profile carbine gas system 14.5" barrel. I plan to turn it down to a similar profile to the Faxon pencil 14.5 middy.

The Faxon barrel gun will have the RCA adj gas key, and the Other will have the suparlative bleed off block. Faxon came with a lightened steel GB, so I will use it for the time being.