Sub 6 with a Twist

I recently added the Scalarworks LDM to my lightest carbine which shed 1.5 ounces from the total weight, lowering it to 6.13 pounds (unloaded). I stood there looking at the scale for moment and realized that I was so tantalizingly close to the 6 pound mark, that I would have to go for it. There are certainly AR-15 builds that are lighter than this but this one is different. It has a bit of a twist that sets it apart from most. I have a set of requirements that I will not compromise in order to maintain this carbine’s intended use as a defensive firearm and the idea for this project was to start with base components that I already owned to show what could be done with careful retrofitting versus building something from the ground up.

JTT Ultralight with a Twist

Throughout the project, these requirements have guided my decisions:

  • It must have an optic, light, back up sights, and a forward grip of some kind (hand stop, vertical grip, etc.). This alone sets it apart from many lightweight builds which are generally done with just an optic or just irons and no light in order to save weight.
  • It must be able to accept a two point sling.
  • It must have a rail that completely covers the gas block (11″ or greater since this is a midlength). This is to support the way I shoot, support practical field shooting positions, and make barricade shooting easier.
  • It must have an appropriate weight buffer (an H buffer in this case) and an M16 bolt carrier group. I do not want to get into adjustable gas systems and lightweight recoil parts.
  • It should have a forward assist… not because I use it often but because I like the idea of it and I have a hard time giving it up.
  • I will not resort to drilling holes in grips, stocks, or similar lightening methods.

Those requirements, coupled with the limitations of using an upper I already had, make this an interesting and challenging project. I could purchase a BCM upper with their KMR and excellent ELW profile barrel and be done but that strays outside my idea for working with what I already had (a BCM 14.5″ lightweight midlength with pinned A2X). I could add a low mass carrier and adjustable gas block and done but that goes against my requirements. So, that basically leaves me hunting and pecking for lighter weight options.

The carbine currently weighs 6.13 pounds which means I will have to find a way to shed a hair over 2 ounces. My current plan is go with a rail system that is lighter than my current Fortis REV. I will probably go with the Fortis REV II since it is about 1.4 ounces lighter than my current REV and uses the standard barrel nut as an attachment point which is important since I have a pinned muzzle device. I will also try to track down the lightest Keymod forward grip I can find. Those two items alone might take me to the sub 6 promised land.

Hopefully, this will serve as some inspiration for what can be done to reduce the weight of the carbine that you already own.
Here is a breakdown of the carbine as it stands:

You can find many of the parts listed above at Brownells. I purchase a lot of my parts there because of the trust they have built with me over the years.

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14 Responses to Sub 6 with a Twist

  1. publiu5 February 9, 2015 at 07:36 #

    What’s the weight on your current handstop?

    • Matt February 9, 2015 at 07:39 #

      .8 oz. If I switch to the Fortis REV II, it will open up the ability to use Keymod on the bottom rail and there are some much lighter Keymod options.

  2. Jesse February 9, 2015 at 08:23 #

    Arisaka Defense finger stop is what you’re looking for.

    • Matt February 9, 2015 at 08:25 #

      I am looking at the Arisaka Finger Stop (it weighs about half of what I use now). The IWC Keymod Hand Stop is also very light. However, I think the KAC URX4 Hand Stop is likely the lightest available.

  3. Dex February 9, 2015 at 11:38 #

    You could save some weight with the MFT flip up sights.

  4. publiu5 February 9, 2015 at 14:10 #

    Ti barrel nut + finger stop may do it. Any idea of weight difference between a Mod3 and Mod4 CH?

    • Matt February 9, 2015 at 14:15 #

      I can’t do the barrel nut. The muzzle device is permanently attached. This upper was chosen for this project specifically because it is light but also because it poses specific challenges. The hope is to show that, even with limitations, a very light carbine can be achieved. Imagine what can be done when building from scratch!

      The Mod 3 versus Mod 4 is a good thought. I’ll have to see how much of a difference there is.

      On paper, I should be able to go under 6 lbs just by switching the rail to the REV II, changing to a lighter forward grip, and using the new lightweight pins from GWACS.

      • Scalarworks (@Scalarworks) February 9, 2015 at 14:35 #

        This definitely inspired us to put together one of our own. A super light weight rifle that doesn’t sacrifice reliability (M16 BCG, H2 buffer, Extra Power Spring). On paper we got our build down to 5.55lbs – that’s with aluminum receivers, 13″ handguard, SF Scout light, and Aimpoint Micro.

        • Matt February 9, 2015 at 14:39 #


          That is totally doable if you are starting from scratch. Someday I will try this same build with a BCM ELW profile barrel and KMR. They are game changers for people who want lightweight builds that are still capable of hard use.

  5. Lucas February 9, 2015 at 15:22 #

    Get some v7 parts that will cut it down.

    • Matt February 9, 2015 at 15:30 #

      There are already some V7 parts in it. The only two addition V7 parts that I can use in this build would be the charging handle and buffer retainer.

  6. tomcattch February 10, 2015 at 07:40 #

    Echo93 isn’t moding the CAV lowers anymore? I can’t find hide nor hair on their site about it.

    • Matt February 10, 2015 at 08:01 #

      I believe they still do. It just isn’t something mentioned on their site.

  7. jerrysimons February 17, 2015 at 20:16 #

    Nice build!

    Matt, you actually helped me build a similar rifle by keeping me up to date on new products, Thanks!
    I first read about V7WS here and I stuck to much of the same theory you espouse when setting up my build parameters. Soon I’ll post another update with more lightweight parts added including ScalarWorks LDM and more V7 parts.
    You may find my weight list helpful (sorry for the crappy format), the .32oz KAC URX 4 handstop is the lightest Keymod handstop I know of.

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