The Sub 6 with a Twist AR-15 build is done (done in the sense that the goal weight has been achieved… I’m sure I will keep tinkering with it)! It now weighs in at 5.94 pounds empty which puts it under the goal weight of 6 pounds. Gun forums are full of pictures of AR-15 carbines that weigh much less than 6 pounds but this build had some unique parameters placed on it as outlined in my original post about the build.
- It must be built using an upper and lower that I already own.
- It must use full weight recoil parts (M16 carrier, H buffer, etc.) for reliability.
- It must have an optic, light, back up irons, a rail that completely covers the gas block, a forward grip, and sling mounts.
I already owned a GWACS Armory CAV-15 Lower that was modified by Echo Nine Three and a Bravo Company USA Lightweight Midlength 14.5″ upper. They were the obvious starting points from among my available uppers and lowers and they gave me a very good starting point for Parameter 1. The main problem that this presented was the fact that the muzzle device was pinned and welded so my handguard options would be limited.
Many of the ultra-light AR-15s that you see in the 4-5 pound range are using lightweight bolt carriers and buffers to reduce the overall weight. I greatly prefer the reliability and durability of the original M16 carrier with a buffer that is properly tuned to the rifle which usually means an H buffer or heavier. In order to stick to Parameter 2, I had to look elsewhere to shed weight.
Most ultra-light AR builds have either an optic or iron sights – not both. They often forgo things like white lights and sling mounting points. Very few have forward grips of any kind or extended rails capable of handling some abuse. Building a carbine that weighed less than 6 pounds but had all of these things meant I was going to have to be picky about accessories and find some ways to save weight.
Those three parameters were chosen to show that lightweight can be achieved with major components that you already have and that you don’t have to go to lightweight bolt carriers, special buffers, adjustable gas blocks, and similar to build a true lightweight. This build also shows that, with careful parts selection, you don’t have to give up gear that makes carbines easier to shoot like forward grips and extended rails.
I should also point out that this carbine was really the result of several years worth of tinkering and parts swapping. While I was hoping to show that you can meaningful weight from the carbine you already own, it should be said that it is cheaper to just build from scratch with the lightest parts you can afford/trust instead of replacing perfectly good parts over time with newer/lighter parts.
The upper used in this build has always been the foundation of my “lightweight” build. It started life with Magpul MOE Hand Guards and a fairly standard lower with IWC accessories and weighed in at right around 7 pounds unloaded and without the sling.
Eventually I shaved the FSB and installed a Troy Alpha rail and when Echo Nine Three worked over one of my GWACS CAV-15 lowers, I moved the upper to that lower. In this configuration, it weighed around 6.5 pounds.
The carbine had reached the stage where only careful parts replacement would shed any meaningful weight. I replaced the rail with a Fortis REV 12. I added a V7 Weapons Systems Forward Assist and Dust Cover. The light and front sight were both replaced with a ROSCH Works SL1 which is a great tool in the lightweight AR builder’s tool chest. Replacing my Aimpoint’s LaRue mount with the LDM from Scalarworks finally brought me to striking distance of 6 pounds. It weighed 6.13 pounds at this stage.
The last push toward the goal weight (pictured earlier in this post) included the new lightweight pin set from GWACS Armory and a Fortis REV II 12″ Rail. The REV II saved 2 ounces over my original REV rail (7.8 versus 9.8 ounces) and allowed me to use a lighter weight hand stop (Knight’s Armament URX 4 Keymod Handstop). This brought the weight to just 5.94 pounds.
The Build List
- BCM Lightweight 14.5″ Midlength Upper with permanently attached A2X and shaved FSB
- LMT BCG
- BCM Medium GUNFIGHTER Charging Handle
- Fortis REV II 12″ rail
- V7 Weapons Systems Dust Cover
- V7 Weapons Systems Forward Assist
- Ladder style rail cover
- Knight’s Armament Company URX4 KeyMod Handstop
- ROSCH Works SL1 (light and front sight)
- Magpul MBUS Rear Sight
- Aimpoint T1
- Scalarworks LDM (Aimpoint mount)
- GWACS Armory CAV-15 Lower modified by Echo Nine Three
- GWACS Armory Lightweight Takedown Pins
- Standard lower parts kit
- Blue Force Gear UWL (sling mount)
- H Buffer
- Standard carbine recoil spring
I don’t really have many additional plans for the rifle. I have been working toward 6 pounds for so long that I don’t want to think about spending another dime on this build. Eventually, I will probably put a Geissele trigger in this build since lighter rifles are easier to shoot with lighter triggers. I may try some addition V7 Weapons Systems parts and I am sure there will be lighter options for things like the rear back up sight that will come along eventually.
Next time you are choosing parts for your AR-15 build, consider weight right along with price and quality. You might be surprised how much weight you can save.