Build Thread My sub 5lb ultralight build

[Jerderv]

Im a backpacker, i enjoy getting out and exploring new places without being constantly reminded im carrying everything i need to thrive for a weekend in the woods. Ounces is pain, i quickly learned that the lighter my pack was the more enjoyable the experience. I wanted to take my experience with using lightweight backpacking gear and apply it to my first AR-15 build.

The goal was to construct a rifle that was as light as i could possibly get it while retaining the simplicity, modularity, and reliability of your standard "mil-spec" AR. Being my first and only ar15 (so far) i would be trusting my life with this rifle. Yes, i wanted light weight, but not at the cost of dependability. Last but not least i wanted to try and keep it affordable, this rifle will be used as a tool and will not be pretty after a few years.

I started shopping and researching around May 2016. I purchased a palmetto state lower and their EPT lpk. I picked up an MOE stock that i promptly modified and a Magpul K grip. I had my lower. I slowly acquired parts for the upper as i decided on exactly what i wanted or found something that would work well on sale. The one thing i new for sure is i was going with a Faxon 16" pencil barrel as their prices, quality, and customer service are awesome.

TL;DR I started with this:

Upper: 53.00oz or 3lbs 5oz or 3.31lbs
Aero Precision no FA upper receiver. 6.2oz
AIM Lightweight NIB BCG 9.0oz
Anderson Mil spec CH 1.0oz
V7 Port door with v7 rod and a spring 0.4oz
Faxon 16" 4150 Pencil barrel 19.4oz
Spikes Melonite gas tube 0.8oz
2A Titanium gas block 0.8oz
ALG 13" V2 handguard 11.70oz
DSA Titanium A2 Flash Hider 1.2oz
Magpul MBUS G2 2.5oz

Lower: 30.8oz or 1lb 14.8oz or 1.92lbs
PSA lower, PSA LPK, EPT Trigger, lightened hammer, ALG Purple hammer spring 18.6oz
Modified Magpul K grip with V7 TI screw 2.2oz
Modified Magpul MOE Stock 5.3oz
Carbine Buffer 2.9oz
Wolf XP Spring 1.8oz

TOTAL RIFLE WEIGHT: 83.8oz or 5lbs 3.8oz or 5.23lbs




I put about 300 rounds through it configured like that i started to learn what i liked and what i didn't like. The rifle had symptoms of being overgassed due to the lightweight carrier but was still 100% reliable. After one of the range trips i disassembled the rifle to find the BCG was flaking, i contacted aim surplus, they apologized and gave me a full refund. I needed a new BCG and i wanted to be able to adjust the gas system. The most affordable way i decided was to buy the AIM lightweight bcg with nitride finish, instead of flaky NIB, and then attach a rubber city armory adjustable gas key. However i stumbled upon a deal i couldn't pass up and ended up getting a regulated 2A lightweight BCG for $300. It was a hard pill to swallow but i knew it was a quality component that i could trust and would give me the ability to turn down the gas and slow down the action.

The new 2A bcg worked well and i was able to actually remove the weights from the carbine buffer. Having the ability to turn the gas down and keep the bolt locked longer made the rifle run smoother and shoot flatter. I was very happy with this setup, however, it wasn't as light as i had hoped for and i found ways to remove weight and improve/maintain reliability.

V Seven Weapon systems offers a number of high quality lightweight nicks and nacks, and i wanted them all! I found a website that ships a lot of stuff for free and decided i would just start replacing steel parts with V7 goodies once or twice a month. This saved me the pain of realizing how much i would ultimately spend on small parts. As the packages arrived the weight of my rifle kept dropping.

I had broken the 5lb barrier. 4lbs 15.4oz


The election was coming up and i new i wanted to grab another lower just in case. I decided i would ditch the PSA lower and swap it for an Aero Precision lower to match the upper. I assembled the PSA lower with all the sparce PSA lower parts that i had replaced over the months. The PSA Spare still needed a few bits so i bought the v7 versions to put on my lightweight rifle and ended up with a functional spare lower while removing more weight from my lightweight rifle.


I still had some more tricks up my sleeve. I did not need nor really use the full 13 inches of handguard. Having modified the pistol grip and stock i felt it was only fitting to continue the trend up front. I had received a TLR-1 HL from my keeper of a girlfriend for christmas. I picked up a poly 3 slot mlok rail section and went about deciding how and where i wanted to run the light. I ended up deciding to leave a small seciont of rail to keep the light out further and retain some room for my hand on the handguard. ALG sells a cowitness top rail and i ordered one of those as well. I made my cuts, filed into shape and sanded smooth. I then painted only where i cut.


Upper:

Aero Precision no FA upper receiver 06.2oz
Faxon 16" 4150 Pencil barrel 19.4oz
2A Regulated BCG 08.0oz
ALG V2 Modified 9 5/8" 06.6oz
ALG EMR Barrel nut and hardware 02.4pz
DSA Titanium A2 Flash Hider 01.2oz
Anderson Mil spec CH w/ v7 latch 01.0oz
Spikes Melonite gas tube 00.8oz
2A Titanium gas block 00.8oz
ALG Co witness rail 00.8oz
V7 Port door 00.4oz
M-lock 3 slot poly 00.3oz



UPPER TOTAL: 48.0oz 3lbs

Lower:

Aero Precision Lower Gen 2 8.2oz
EPT Trigger, mil spec spring, discon, pin 1.2oz
EPT Hammer, modified, alg purp spring, pin 1.0oz
V7 Take down and pivot pins Aluminum 0.2oz
V7 Safety 3 gun hybrid AL/TI 57* RH 0.3oz
V7 Bolt catch S7 tool steel 0.3oz
V7 Mag catch Aluminum 0.2oz
V7 End plate Aluminum 0.2oz
V7 Castle nut Aluminum 0.3oz
V7 Buffer tube 3.5oz
V7 Ti Buffer retainer 0.1oz
v7 Ti Grip screw 0.2oz
Gutted Carbine buffer 1.0oz
Tubb's SS .308 spring trimmed 2.0oz
Modified Magpul MOE Stock 5.3oz
Modified Magpul K grip 2.0oz
Magpul poly Trigger guard 0.3oz



LOWER TOTAL: 26.3oz 1lbs 10.3oz


LOWER+UPPER TOTAL: 74.3oz 4lbs 10.3oz


Magpul MBUS G2 2.4oz


RIFLE TOTAL:______76.7oz______4lbs 12.7oz______4.8lbs______


This is where im at now. It shoots great, its 6lbs 2oz with sling, light, and a loaded 20rnd pmag. The barrel has had about 800rounds through it. Another great thing about this setup is that it has a standard gas port in the barrel and a fixed gas block so i can just drop a FA bolt carrier and carbine buffer/buffer spring in for ultimate reliability.

Thanks for looking!

Read More

 

[The Heretic]

I am thinking of trying out the 80% route, while also trying to stay as lightweight as possible. I would probably get three 80% lowers (I am thinking maybe DSA?) as I always get such things in threes (3 people I prep for including myself).

I am thinking of having the lower be declared a pistol lower, then I can go with a lightweight 12" to 14" (including flash hider) pencil profile barrel and lightweight parts. I would not be going with 5.56x45 as 5.56 just gives up too much velocity in the shorter barrels - later I would maybe get an upper with a barrel between 16" and 20" for a 5.56.

Maybe 7.62x39 or .300 Blackout, probably the former - although I already have 7.62x39 rifles. That's the nice thing about the AR platform - fairly easy to swap out uppers.

The other thing I was thinking of was the Echo trigger with their BCG.

Then there are always the belt-fed uppers - but I am thinking if I am going that route then I would prefer it be in 7.62x51 instead so that would mean a larger lower/etc.

 

[Jerderv]

Cool, you should make a build thread for your rifles.

 

[IronMonster]

Am I the only one not seeing all the pics? I see some but not others (there is a placeholder)

Great write up by the way

 

[Joe Link]

Nice build! I'm slowly putting together parts for a lightweight build of my own. Those 2A BCG's sure are $$$

Am I the only one not seeing all the pics? I see some but not others (there is a placeholder)

Great write up by the way

Nope, same issue for me.

@Jerderv did you link them from another site?

 

[Jerderv]

Odd, ill upload with a different host.

 

[Jerderv]

Oh and i bought a new trigger, Spikes tactical enhanced battle trigger.

 

[Robert3000]

Thanks for the idea. Not something for now, but it'd be great to go as light as possible.

 

[Jerderv]

Modified the stripped buffer further, got it down to 22grams or 0.8oz.

 

[Jerderv]

Aim lightweight nitride BCG came back in stock. Had the RCA adjustable gas key already so i went ahead and snagged one. As usual they sold out very fast so im glad i went for it. Got the key mounted this morning. This setup should work just as well as the 2A bcg but at a third of the price. I also now have a full weight carrier/carbine buffer that i can drop in for the zombie apocalypse.

 

[IronMonster]

So how is it running now with these mods?

 

[Jerderv]

So how is it running now with these mods?

The skeletonized buffer was a success! Im running it with the trimmed down Tubbs .308 flat coil spring.

The 2A carrier is awesome and has been running great since i got it, it can be adjusted whenever by loosening the lock screw and turning the gate through the ejection port. I really like this carrier and 2A stands behind all their products with amazing customer service.

The AIM carrier and RCA key i don't have many shots through yet. I only set it up today and shot probably about 20 rounds with it. The gas key works well to increase the dwell before the bolt unlocks. It shoots really smooth with this setup and im impressed with its performance (so far) for the price tag. I need to get some more ammo through it before i really make up my mind. One thing i have read is that the adjustment screws in the key will seize up after a while so its best to get it set to cycle with the weakest ammo you plan on shooting and then just expect it to fuse itself together.

The PSA full weight carrier with a standard car buffer and car spring shoots as expected. It recoils more and dips the barrel more but its "proven" so im glad i have it laying around.

I like this rifle a lot. I put 40 rounds of PMC .223 and 60 rounds of fed xm193 through it today. So far this rifle has been %100 reliable for me.

 

[KeepnitReel]

So how you keeping the buffer weight in that buffer

 

[Jerderv]

So how you keeping the buffer weight in that buffer

Well its not really a buffer any more, its more of a spring guide at this point. There are no weights, im just running the shell.

The action in these firearms is a system and changes can be made as long as you understand why they are there and how the performance will be affected when you remove or modify things. There is a lot of design that went into the standard setup to make it reliable for all conditions. The buffer, with its free floating weights, was mainly to prevent bolt bounce to help avoid light strikes during full auto fire. If you are not trying to fire 800rpm then you dont really need a buffer. However, that weight helps increase the dwell time between when the primer is ignited and the case extraction starts. You can not and should not remove weight from the action without the ability to increase that dwell time via a different method. Many choose to use adjustable gas blocks to accomplish increasing the dwell time. I chose to use adjustable gas keys and carriers. By restricting the gas flow into the carrier you slow down the rate at which the gas fills the piston chamber in the carrier and unlocks the bolt. Extraction starts once the bolt is unlocked. Once you have a method of delaying extraction via the gas system you can start to remove weight from the buffer and carrier. I chose to use a stronger recoil spring to also aid in delaying extraction. I like tinkering with things, needless to say im having fun playing with these setups.

 

[KeepnitReel]

Roger that, I too run adjustable gas blocks in both my rifle lengths and SBR's. I guess I never really saw it mechanically that way. I use it to reduce blow back and extra gas not needed to completely cycle the BCG. I measure it more in reduced recoil, never thought I could start to reduce weight.

Interesting................

You must have that thing turned all the way down in gas pressures then. Your not getting major buffer weight impacts at the end of your buffer tube ?

I would think you would want a little bit of weight in the buffer to have the mass needed to completely seat the next round in the chamber.

Interesting ,,, opened my eyes tonight. Nice

 

[Jerderv]

Roger that, I too run adjustable gas blocks in both my rifle lengths and SBR's. I guess I never really saw it mechanically that way. I use it to reduce blow back and extra gas not needed to completely cycle the BCG. I measure it more in reduced recoil, never thought I could start to reduce weight.

Interesting................

You get it! There are so may variables in all these parts, barrel length, gas port size, etc. The ability to set the gas system to work with your particular parts is hugely beneficial. People forget that the the AR platform IS a piston gun. The piston is in the carrier. The bolt will not move backwards due to chamber pressure alone. The bolt only unlocks and moves backwards once gas is blown into the piston chamber. Then the carrier moves backwards to twist and unlock the bolt.

You must have that thing turned all the way down in gas pressures then. Your not getting major buffer weight impacts at the end of your buffer tube ?

It is turned down pretty far, I start with the gas turned all the way off. I slowly increase gas into the piston chamber once the bolt is unlocking from battery and there is enough gas to still push the carrier back far enough to reliably lock back on an empty mag. The buffer, spring guide at this point, isn't impacting the end of the buffer tube any more than normal setups. Reason is i have delayed how quickly the bolt unlocks and this in turn results in a lower carrier velocity because chamber pressure/gas line pressure has dropped. Im also running a stiffer spring and that assists with controlling the unlock time and the carrier velocity.

I would think you would want a little bit of weight in the buffer to have the mass needed to completely seat the next round in the chamber.

Yes, the mass of a normal FA and 3oz carbine buffer setup does help ensure the bolt doesn't slow down to much when stripping a round from the magazine. This is part of the reason why i chose to run a stiffer action spring.

Interesting ,,, opened my eyes tonight. Nice

I'm just passing on what others have taught me.

 

[Kruel J]

Super cool build! Gives me some ideas!

 

[Jerderv]

Yah so be forewarned, building a lightweight rifle can put a pretty big smile on your face and everyone you hand it to. I cant wait to to take this with me on some backpacking trips.

Heres a super awesome spreadsheet that "jekbrown" on ar15.com put together. AR15 LW Parts List

This is where i got most of my inspiration
ULTRA light weight picture thread....the under 6 crowd. - AR15.COM

 

[KeepnitReel]

Awesome info there.. Thank you

Well its not really a buffer any more, its more of a spring guide at this point. There are no weights, im just running the shell.

The action in these firearms is a system and changes can be made as long as you understand why they are there and how the performance will be affected when you remove or modify things. There is a lot of design that went into the standard setup to make it reliable for all conditions. The buffer, with its free floating weights, was mainly to prevent bolt bounce to help avoid light strikes during full auto fire. If you are not trying to fire 800rpm then you dont really need a buffer. However, that weight helps increase the dwell time between when the primer is ignited and the case extraction starts. You can not and should not remove weight from the action without the ability to increase that dwell time via a different method. Many choose to use adjustable gas blocks to accomplish increasing the dwell time. I chose to use adjustable gas keys and carriers. By restricting the gas flow into the carrier you slow down the rate at which the gas fills the piston chamber in the carrier and unlocks the bolt. Extraction starts once the bolt is unlocked. Once you have a method of delaying extraction via the gas system you can start to remove weight from the buffer and carrier. I chose to use a stronger recoil spring to also aid in delaying extraction. I like tinkering with things, needless to say im having fun playing with these setups.

Yah so be forewarned, building a lightweight rifle can put a pretty big smile on your face and everyone you hand it to. I cant wait to to take this with me on some backpacking trips.

Heres a super awesome spreadsheet that "jekbrown" on ar15.com put together. AR15 LW Parts List

This is where i got most of my inspiration
ULTRA light weight picture thread....the under 6 crowd. - AR15.COM

 

[KeepnitReel]

Aim lightweight nitride BCG came back in stock. Had the RCA adjustable gas key already so i went ahead and snagged one. As usual they sold out very fast so im glad i went for it. Got the key mounted this morning. This setup should work just as well as the 2A bcg but at a third of the price. I also now have a full weight carrier/carbine buffer that i can drop in for the zombie apocalypse.
View attachment 339771
View attachment 339772

What does the adjustable gas key do that the adjustable gas block can't? That's where your setting your dwell timing on the bolt unlock ? Your talking milliseconds ..... interesting.