Project Überlight: sub 4lb SBR; sub 5lb suppressed.
Following on the heels of my successful project Noveske Ultralight I was bitten by the lightweight bug. https://www.m4carbine.net/showthread.php?146386-Noveske-Ultralight-(Update)
That sub 6lb ultralight home defense rifle was built balancing parameters favoring reliability and key features of a HD rifle as is documented in the thread. It also took awhile as it was on the front end of the ultralight craze (and in fact it continues to be updated), but already by its finish, I had in mind what it would take to make a radically lightweight rifle by prioritizing lightweight above all else. Certainly the idea was obsessive and possibly insane but it would be enjoyable. The goal for Project Überlightlight was to build the lightest rifle possible using the strategy of compounding weight savings through combined ultralight parts selection. Sub 4lbs/64oz was the ultimate target weight even though I knew it was a long shot.
Build parameters had to be set out of the gate for parts selection.
- I wasn’t going to use custom, one-off or non-commercially available parts. Largely V7 Weapon Systems, 2A Armament, and BCM made this possible.
- The priority of lightweight meant the rifle would be relegated to the realm of a range toy, which allowed for experimenting with ultralight parts to that end (ultralightweight carrier, buffer, etc.).
- No cheating! When weighed, the rifle had to have at least one sight system and include the attachments with which it would be used (QD sockets, etc.).
Even with these parameters set, the build floundered. I had been working on it for over a year and have at times waited for months on parts to be released only to change direction. The problem I ran into was the thing is a huge money pit and it actually needed more direction than simply the lightest range toy possible. Originally Überlight was going to be a 14.5" Mid BCM ELW-F 556 barrel with pinned V7WS extended A2 v-grooved flash hider, 10" KMR rail, and slick side upper–but that was too close to what I already did with Noveske Ultralight and not enough lighter to be worth it. At that point, going short barreled rifle was the clear path to take; an 11.5" BCM ELW-F barrel was the plan. Shorter, lighter, and different. Yet still, SBR wasn’t enough. If I was going to dump money into a range toy the rifle needed to be an exceptional range toy, not just an insanely lightweight rifle that still went bang. I wanted Überlight to wow it was so light and also be fun to shoot, otherwise it was not worth it. That is when .300blk emerged as the clear choice.
300blk is designed for complete powder burn down to 8" of barrel length allowing for further weight savings using sub 10" barrels without creating an abomination. Also, for a given barrel profile, a 30cal barrel is actually lighter than a 556 barrel due to less wall thickness. The problem is most short barrels have heavy profiles and end up only being a little lighter than longer, lightweight profile barrels. This did not fit the strategy of compounding weight savings and would simply not do. That’s when V7WS released their 8.25" .300blk barrel with a modest profile and a fluting option: 15.15oz stripped. Perfect! But what 7" rail to use? BCM’s magnesium alloy KMR is the defacto go-to ultralight rail system especially when combined with V7WS titanium KMR barrel nut and hardware. Thankfully I didn’t have to wait long as BCM made a surprise announcement that the 7" KMR was available around the same time I purchased the barrel. Überlight finally came together with a clear direction and, surprisingly, right at the sub-4lb target weight.
Parts List, Phase 1: 63.5oz
Upper:
-2A Armament Balios-lite 7075 billet slick side upper receiver
-V7WS 8.25" .300blk stainless steel barrel
-V7WS .750" titanium set-screw gas-block
-Spike’s Tactical Melonite pistol gas-tube
-V7WS titanium 762 Furion Muzzle Brake
-BCM KMR magnesium alloy 7" rail
-V7WS titanium KMR barrel-nut (soon to add titanium KMR clamp blocks)
-V7WS lightened mil-spec charging handle
-V7WS aluminum ultralight port-door
-V7WS aluminum port-door rod
-V7WS headspace matched melonite 9310 bolt
-Boomfab Titane titanium bolt carrier
-RCA melonite gas-adjustable carrier key
-RCA melonite firing-pin
-V7WS 4340 melonite cam-pin
Lower:
-2A Armament Balios-lite 7075 billet lower receiver
-V7WS first run 7075 carbine receiver extension
-Battle Arms Development BAD-LBS-MIL 7075 billet butt-stock
-V7WS aluminum end-plate
-V7WS aluminum alloy castle nut
-Taccom ultra-lightweight deralin AR15 carbine buffer
-SpringCo white carbine spring
-V7WS titanium buffer retainer
-V7WS aluminum alloy pin set
-V7WS S7 lightened bolt catch
-V7WS aluminum alloy mag catch
-V7WS aluminum mag release button
-V7WS titanium core, aluminum lever rightside 57* safety selector
-Magpul original K grip
-V7WS titanium grip screw
-Geissele SD3G trigger
-V7WS titanium Geissele trigger pins
Attachments:
-Trijicon RMR RM06 adjustable 3.25moa dot RDS sight
-LaRure Tactical LT827 RMR lower 1/3rd QD mount
-Spikes Tactical aluminum Billet Micro Folding Sights w/ titanium bolts
-V7WS aluminum BCM keymod QD socket
-Noveske NSR single keymod handstop (adds .2oz, not pictured)
The rifle shoots great! This configuration is amazingly handy and surprisingly balanced in it’s shortness. The V7WS Furion brake is quite effective at mitigating recoil and helps with some of the snap of the superlight reciprocating assembly. Adjustable gas was a necessity with this set-up as the total weight of the Boomfab Titane carrier and Taccom ultralight carbine buffer is only about 5.1oz. FTF malfunctions due to excessive BCG speed is a concern as well as increased gas blowback from high chamber pressures with quick bolt unlock. In order to save weight using the V7WS titanium gas-block the RCA adjustable gas-key was the best solution. The key is the same weight as a mil-spec gas-key and fit on the ultralight Boomfab Titane carrier, 4.4oz w/ key. After messing with the adjustable gas-key I had subs reloading without locking back on empty and supers shooting with full function. The subs with the brake and gas adjustment were ridiculously soft shooting, but who builds a .300blk SBR range toy without provision for suppressed subsonic loads? Enter Phase 2.
Parts List, Phase 2: 76.9oz
-SilencerCo Omega 762 direct thread silencer
-DSArms CAR type Fiberite stock (Colt CAR N1 clone)
The SilencerCo Omega is an excellent match for his build. SiCo struck a great balance between durability with the stellite blast baffle and lightweight with the titanium tube and stainless steel baffles, resulting in a full-auto rated can weighing only 13.35oz mounted*. Testing with 100 rounds of Remington UMC 220gr .300blk through the can was 100% without changing the gas settings on the key mentioned above. Due to the faster carrier speed of the lightweight set up and faster unlock time, I was getting quite a bit of gas in my face suppressed, especially shooting supers (Fiocchi 150gr .300blk). I think for the next outing I will adjust the gas-key to shoot supers unsuppressed with full function but to not cycle with subs unsuppressed (who shoots subs without a can anyway?). This should give me the best gas mitigation I can get with the set up. Though I am not sure if regulation at the carrier key will cut down on blowback much anyway. I imagine more gas escapes from the upper receiver than would if regulation at the gas-block kept gas from entering the gas-tube in the first place, since the gas is already in the gas-tube pressurized when the gas-key uncovers the gas-tube as the carrier moves rearward. Many companies are working on products that regulate at the gas-key (SunDevil Mfg, RCA, 2A Armament, Gemtech), I am curious what their testing has shown.
-Omega stripped w/o mount or end-cap insert: 9.75oz
-Omega/Harvester Big Bore 5/8X24 direct thread mount: 2.2oz
-Omega/Harvester Big Bore ASR mount (adds .825" OAL over direct thread mount): 3.45oz
-ASR Muzzle Brake 5/8x24 762mm: 3.65oz
-ASR Muzzle Brake 1/2x28 5.56mm: 4.0oz
-Omega 762mm flat end-cap (ferrous): 1.4oz
-Omega Anchor Brake end-cap (nonferrous, adds .9" OAL over flat end-cap): 1.5oz
Totals:
-Omega with ASR mount and Anchor Brake end-cap: 14.7oz & about 8 inches OAL ( minus .1oz and .9 inches for flat end-cap)
-Omega with 5/8x24 direct thread mount and 762 flat end-cap: 13.35oz & about 6.25 inches OAL ( add .1oz & .9 inches for Anchor Brake end-cap)*
[suppressed subs video] coming soon
Parts comments:
-BAD-LBS-MIL w/ V7WS parts (7.2oz) vs. ACE AR-UL-E (9.15/6.55oz)
The 3.2oz BAD-LBS-MIL is not necessarily revolutionary but it does offer some advantages over the similar ACE AR-UL-E set-up. First, the BAD-LBS-Mil has the integral QD socket. Second, despite the AR-UL-E being lighter when minimally configured (6.55oz) the BAD-LBS-MIL attaches to a standard buffer tube, which allows for swapping out an adjustable stock with just a simple bolt. Because lets be frank, the LOP sucks with just a carbine buffer tube and there are times you want the adjustment of a real stock. With the V7WS .4oz end-plate/castle nut combo, and 3.6 oz carbine buffer tube, the total weight is still only 7.2oz with the BAD-LBS-MIL 3.2oz stock. The flexibility of swapping an adjustable stock is also the main reason I did not consider the 6.9oz (spec) Sabertube, QD end-plate, BAD-LBS combo, despite it having a longer fixed LOP http://www.battlearmsdevelopment.com/sabertube-tm-qd-end-plate-bad-lbs-lightweight-stock-combo
–AR-UL-E fixed carbine stock assembly: 9.15oz, 6.55oz minimally configured
receiver extension tube: 2.65oz
foam pad: .55oz
gusset/clamp w/ screw: 1oz*
sling mount (w/o additional plug screw): .35oz
clamp-on butt w/ screw: 2.9oz*
rubber butt pad w/ screws: 1.7oz
–RCA adjustable gas-key vs. SunDevil MFG adjustable gas key (same weight)
One complaint about the RCA gas-key is there is not enough threads in the key for the lock screw to solidly engage if the adjustment screw is backed off most of the way, i.e. little regulation means the lock screw only has about 1 twist into the key before bottoming out on the adjustment screw, which is not enough to tighten it well and not enough for loctite or rockset. Though it is not an issue if the adjustment screw is threaded in for more regulation as there is more room for the lock screw to thread in behind it. Originally I thought the RCA lock screw design was a big improvement over the SunDevil Mfg key with only one screw and a nylon friction detent since the one screw can not be adjusted as desired, then removed, loctited and reinserted to the exact same position (I think SunDevil intends the nylon friction detent to be sufficient securement), but depending on how much regulation you want, the RCA key may not work for you. Believe me, you do not want that lock screw to come loose in the upper! I got lucky that it only wedged underneath the trigger and put me out of service for 15min while I frantically figured out why the trigger in my SBR lower went dead!
thread: https://www.m4carbine.net/showthread.php?150517-New-Drop-in-adjustable-gas-system
–Boomfab Titane titanium bolt carrier (4.4oz w/ key) vs. JP LMOS aluminum bolt carrier (3.76oz w/ key)
So the JP LMOS aluminum bolt carrier is lighter than the Boomfab Titane titanium carrier. Call me crazy to spend that much on a bolt carrier but come and lock me up if I spend the same on a carrier said to be a consumable wear item as particulate and hot gasses blast the aluminum while steel gas-rings grind on it. JP specifies the aluminum LMOS is intended for games guns with mid-length to rifle gas-systems http://jprifles.com/buy.php?item=JPBC-1 .300blk with pistol gas was too much of a gamble with the money, though I would happily test one out if JP wanted to sponsor it! 
–Trijicon RMR RM06 primary RDS vs. Aimpoint Micro primary RDS
Previously I compared these two lightweight RDS solutions with regard to a defensive rifle. The clear winner for that use is the 3.05oz Aimpoint Micro mounted on a 1.3oz ScalarWorks LDM QD micro mount (or a fixed 1.3oz Fortis F1 mount before the LDM). The older 3.65oz RM34 and 3.5oz ADM RMR QD mounts were so heavy that the Aimpoint Micro mounted was actually lighter than the 1.25oz RMR mounted, making the choice even more obvious. But the new Larue Tactical LT827 QD RMR mount has changed that as it weighs only 2.35oz. Mounted, the 1.25oz RMR on a 2.35oz LT827 is lighter at 3.6oz than a 3.05oz Aimpoint T1 mounted on a 1.3oz ScalarWorks LDM for 4.35oz total. While the Larue mount is exceptional in quality and is unique with a lower 1/3rd co-witness that opens up the view of the tiny RMR window, there are still too many feature draw backs with the RMR to consider it over an Aimpoint Micro for defensive use, IMO. The optical distortion, among other features, of the RMR is poor in comparison to the Micro. Project Uberlight, however, does not have the same defense requirements, so since the RMR mount on a LT827 is lighter, it went on the gun. However, looking at the 1.3oz weight and the quality of the ScalarWorks LDM QD and Fortis F1 fixed Micro mounts, there is no reason a RMR mount couldn’t be made weighing 1oz or less with the same quality. I am still waiting on this to happen and will switch when it does. The RMR is still a good sporting primary RDS or secondary defense RDS especially among other open micro reflex sights.
-Aimpoint T1/ Fortis F1 combo (4.35oz) vs. Trijicon RMR/ RM34 mount combo (4.9oz measured)
I considered the RMR but decided the T1 was better and, surprisingly, is lighter when mounted. The T1 mounted on a Fortis F1 weighs 4.35oz measured (3.05oz+1.3oz). The RMR only weighs 1.25oz but the RM34 mount weighs 3.65oz and the ADM RMR mount weighs 3.5oz, for a mounted total of 4.9oz and 4.75oz respectively. In both cases the T1/F1 is lighter. As far as features go, I would rather have the T1/F1 combo with 2moa dot, mounted battery changes, longer battery life, 1/2" at 100yd click adjustment (vs 1"@100yd), lower 1/3rd co-witness, and a proven track record. But, unlike the RMR, the lightest T1 mounts (Fortis F1 1.3oz and DD Micro 1.7oz) are not QD. But I decided QD wasn’t wholly necessary on a dedicated HD/nightstand rifle after watching the DD torture test video; my T1 will survive where I will not. Short of taking a round directly to the optic, the only thing it is realistically susceptible to is fog and rain, but inside the house should not be a problem there. [UPDATE] ScalarWorks LDM micro QD mount has changed the game. It is no compromise at the same weight as the lightweight fixed Fortis F1 mount but with a true quick detach securement. Thank you ScalarWorks for setting the bar!
Someone really needs to make a lighter mount for the RMR on the order of 1oz or less, something like the Fortis F1 or ScalarWorks LDM scaled down to the size of the RMR would be perfect and scary light (if strength was a concern it could be made out of the aluminum alloy V7 uses). The weight benefit of the RMR might be worth the feature trade off at 2.2oz mounted. [Update] The Larue Tactical LT827 QD RMR mount is the current lightest RMR mount at 2.35oz. It is exceptional quality and is much lighter than the ADM and RM34 mounts and actually places the RMR in almost a lower 1/3d co-witness. However, the feature drawbacks of the RMR still do not beat out an Aimpoint Micro on a ScalarWorks LDM, even though the LT827 and RMR combo at 3.6oz is finally lighter than the ScalarWorks LDM/Aimpoint Micro combo at 4.35oz. A lighter RMR mount is still needed to balance out its drawbacks
–2A Armament Balios-lite billet lightweight receivers vs Battle Arms Development billet lightweight receivers
2A Armament takes the cake for lightweight receivers. Their machining is perfection and the lightweight cuts do not look overly busy aesthetically. BAD also makes a lightweight receiver set but it is not quite as light as the 2A Armament set and does not look as nice, IMO. BAD also has a version of their receivers available only on the special edition OIP rifle but that set is not available for purchase and weighs the same as the 2A Armament Balios-lite set (with the tension screw removed), yet it does not have a full top rail and has lightning cuts that I personally find visually displeasing and unnecessary in comparison.
What about Mag Tactical’s cast magnesium receivers? I value my eyesight too much to risk using a cast magnesium upper and there is no way I would SBR one of their lowers. Tennessee Arms Co makes a nylon lower receiver with brass reinforcements that is exceptionally light but at this time I am still evaluating if their lowers are something I would consider SBRing. Even so, I probably wouldn’t replace the Balios-lite lower on this project as it is excellent and matches the upper.
–Spike’s Tactical Micro Sight Set (1.9oz) vs Bobro lowrider sight set (1.7oz)
Spike’s Micro sights thread:
https://www.m4carbine.net/showthread.php?147745-New-Spikes-Tactical-Flip-up-BUIS/page3
I was not very impressed with the Spike’s sights in comparison to others but for a ultralight .300blk build they are great and the somewhat goofed adjustable elevation is still nice given the low velocity of the round. For comparison the Bobro lowrider sights each weigh .85oz for a total of 1.7oz, but I already had the Spike’s sights laying around, so they went on the build. I may take the sights off the gun and just run the RMR but weight was made with the sights so there is not much of a reason to remove them.
Big thanks to V7 Weapon Systems, Bravo Company USA, and 2A Armament, among others listed above for their innovative parts making this build possible. I would like to point out nothing about this build was sponsored. I am not affiliated with any of the companies from which I sourced parts. My opinions are my own. Thanks for viewing!
