Started building a lightweight AR and finding specs isn't always easy plus are they true or not??   So I wanted to jot down my findings for others.  Plus I'm a weight nut, comes from bikes and cars.  

This build is just what I can afford and what I want.  I know I can do lighter.

Lower....
Anderson lower, typical, nothing fancy- 8.68oz
CMMG lower parts- 2.00oz
PSA mil spec trigger and pins- 2.53oz
ATI buffer tube- 3.47oz
ATI castle nut- 0.52oz
ATI end plate- 0.49oz
ATI buffer- 2.95oz
ATI spring- 1.85oz
MFT stock- 6.02oz, 5.8oz advertised
MFT trigger guard with roll pin and front allen screw- 0.20oz
MFT EPG16 gutted grip- 2.24oz, 2.4oz advertised with insert, roll pin and trap door
Magpul 1/4-28, 1" grip bolt- 0.23oz
Total- 31.18oz
Actual weight on my scale- 31.24oz probably from oiling?  




Some upper parts on the way, will weigh later

Upper....
Faxon 14.5" pencil barrel- 18.24oz, 18.4oz advertised
Faxon QPQ LWT BCG- 8.48oz, 8.5oz advertised
2A Armament BALIOS lite upper- 5.79oz, 5.85oz advertised
2A Armament 10" keymod rail with "upgraded" aluminium barrel nut- 6.41oz, 6.35oz advertised
VSeven titanium 0.625" gas block- 0.71oz, 0.68oz advertised, VSeven does not state 3 set screws weight
Strike poly dust cover- 0.40, 0.30oz advertised
LBE charging handle- 1.12oz
Mid length gas tube with roll pin- 0.76oz, 0.64oz online source gas tube only
Precision Armament M4-74 silver comp- 2.67oz
Crush washer- 0.11oz
Magpul flipup sights- 2.47oz
Total- 47.16


EDIT...............
Vortex Venom mini red dot- 1.61oz
Pinned upper added 0.04oz
Total upper- 46.34oz

Total AR-15- 77.58oz, 4.85lbs

Sounds like a great build in progress.

syno:  You are doing great on the upper half, but the lower assy is way too heavy IMO.  It needs to be closer to 20 oz.  Check out the combination receiver extension/fixed buttstocks from Smoke Composites.  You give up the length adjustment, but my carbine sized model weighs only 4 oz.  Add to that a 1 oz buffer and reduced strength spring from Taccom.  Also, with the reduced mass in the carrier and buffer, you need adjustable gas to keep the bolt speed down.  I like the adj. gas blocks from SLR and the adjustable gas keys from Rubber City, take your pick.  The keys are cheaper but the gas blocks are easier to tinker with. good luck - CW

Everything is bought at this point so I'm going to have to play it by ear and see what happens.  Again I just wanted a rifle under 5lbs and what I could afford buying here and there so that's where some of these parts came from.  Barrel shows tomorrow so we'll see what my weight is!

Well you're under 5lbs w/o sights or mag.
You can always add lighter parts down the road and of course the removed parts will be the start of another build! That's the rules.

I have sights, no mag.

Updated the list with the first batch of parts that arrived.  Pretty happy with some like Faxon that came under what's advertised but the others were over.  The Faxon stuff is awesome!  The BCG is crazy light!  Should still be a sub 5lbs rifle though.  Also the total length looks safe at 16.75" with the comp I chose.  

Faxon 14.5" barrel- 18.24oz, 18.4oz advertised
Faxon BCG- 8.48oz, 8.5oz advertised
Vseven Ti gas block- 0.68oz, with 3 set screws 0.71oz, 0.68oz advertised
Gas tube with roll pin- 0.76oz
Strike poly dust cover- 0.40oz, 0.30oz advertised
YHM crush washer 0.11oz

Thanks.  How confident are you your barrel and BCG don't need headspaced checked?

OP: That's a nice setup so far. Here is my lightweight (not ultra LW) range build so far at 4 lbs. with MBUS, but without mag, but I'll be making changes this weekend:

Faxon 4150 QPQ 16" mid pencil w/ thread protector
AIM Surplus low mass BCG (8.9 oz w bolt)
Superlative arms .675 adj. gas block
Aero Precision standard (not M4E1) upper w/ FA and door (blem)
Aero Precision 9" MLOK guards with their barrel nut (blem)
Magpul MBUS v2 sights

NFA poly lower with NFA steel/poly LPK pre-installed
Carbine buffer tube with standard spring, castle nut, end plate
MFT minimalist stock
1 oz empty buffer with single alum. weight

Last weekend, I put 200 rounds through it, with 5 different types of ammo (55gr and 62gr), including Tul and Cabelas "Hipshot" and tuned the gas block to cycle all. Works great, no FTEs or short stroking.

Changes coming up:

I have a lighter DSA lightweight upper coming, that should be 5.8oz. I'll have to go back to my notes, but that AP upper was not very light, over 8 oz I believe.
I'll also be replacing the AP 9" guards which don't cover the gas block with 12" guntec handguards with alum barrel nut that weigh about the same as the AP 9"
I'll be replacing the lower NFA lower with a Mag tactical lower with either CMMG or Anderson LPK to start with. This might add some oz, but I might be OK, even if the weight goes up.

I have a < 2 oz muzzle brake, but the lwbcg, low weight buffer, and adj. gas, I have it tuned to feel like a 10/22. I'm concerned the muzzle brake would add blowback to my fellow range folks.

Probably have about $700 into the way it is now, have avoided any exotic pricey V7 parts so far, but might look into their end plate or parts that give the most reduced weight value.

Ok everything this here, let's finish this!!

2A Armament 10" key rail with titanium nut/ rail- 5.28oz, nut 1.80oz, total- 7.08oz, advertised- 7.00oz
2A Armament aluminium barrel nut- 1.13oz, adertised 1.10oz
2A Armament lite BALIOS upper- 5.79oz, advertised 5.85oz
LBE charging handle- 1.12oz

Pics to follow!!!!

All done!  78.4oz, 4.9lbs!  So light and awesome.  Compare this to the rifle I just finished last week with a 20" heavy barrel that weighs 11lbs!  This rifle is half the weight, feels half the length, barrel size, rail size etc!  Still love both though.  

First time to the range with my two new ARs that I built.  Yeah I am pretty happy with the 11lbs monster 20 inch heavy barrel AR sighted in at 25 yards with no adjustment to elevation and just a few clicks for windage (not bad for an eye ball install).  First pic is a 3 shot group with factory 55g 5.56 ammo and it had a few rounds through so the barrel was warm.  Cant wait to shoot 100yrds and longer!  

The 4.9lbs AR with magpul flip up sights, not so much haha.  Now i didnt have my elevation tool on me so the height wasnt my problem.  Needless to say, scope helps a bit.

Looks good.
Thanks for the list. Even though my parts will be completely different, it's always helpful to see what parts were used.

I'm building a lightweight for my wife but I don't have the income to match my desire to build these rifles, so mine won't be anything exotic - just "lighter than average".

The barrel weight is a huge factor and I'll also be using a Faxon pencil barrel - I'm still undecided on the length. 16"? 14.5" with my own muzzle device pinned? One of the Faxon 14.5 with slim, pinned muzzle device? I'd love to try the new Faxon pinned comp barrel, but I don't know how effective it is. Since I'm building it for my wife, the effectiveness of a comp/brake is more important than if I were building it for myself.

Anyway, other than the barrel, my only other "light" part will be the one piece lower/stock in the form of a GWACS CAV-15 "polymer" lower.
They say that once the LPK, buffer and spring are installed, it's a full pound lighter than a "standard" complete lower with stock.

I have an Anderson Sport upper with no FA or dust cover. I have the LPK and buffer/spring to finish the lower.
All I really need now is the barrel, purple ALG Defense hand guard, and a BCG (considering the AIM lightweight BCG)

Shouldn't be too long now...

Update

Decided once again I do not like the Magpul MBUS flip ups.  Went with the Vortex Venom red dot instead which comes in at 1.61oz with mount which saves 0.86oz over the flip ups.  

Total upper now weighs 46.34oz which means the steel pin and weld added 0.04oz.  The AR now weighs 77.58oz or 4.85lbs.

60kpsi? That's a fun fact I learned today....that's more than I thought. Do you guys do any FEA stress/nodal analyses?

Nice pair of builds. 1 rifle, 1 carbine. That's how I jumped in, I bought a pair myself.
Not bad shooting at all, first time out. Good results with no major problems to report that's excellent. -CB

Thanks.  Carbines the smallest right?  The LWT build is a mid length.  I probably coulda saved weight doing a carbine.

Last update!!

Saved a little more weight.  The PSA mil spec trigger if I had to guess was around 8-10lbs of pull.  The 2 surfaces are very well polished but the springs are super heavy!!  I decided to drop in the JP Enterprises yellow spring kit for like $11 to help out which is rated at 3.5-4.5lbs.  Also incase of light strikes I bobbed the tail of the hammer to reduce weight because of the lighter springs.  I fired two primers off without powder or a bullet and the strikes look pretty deep.   So I don't think I will have a problem.  The pull is now lighter than my POF precision single stages which are rated at 4.5lbs.  This setup is definitely in the 3lbs range now.

The lowers total weight is now 31.01oz making the total rifle now 77.35oz or 4.83lbs.

e

synolimit,

Your hammer spring is installed backwards.

Yes, a carbine is usually a shorter barreled version of an existing rifle. Not always. For Ar-15's the collapsible or fixed stock is a quick indicator. The gas system length, carbine midlength or rifle isn't usually a factor -CB

You made the right move using midlength gas system with a lightweight build. Midlength gas is a little easier on the gun/parts. A carbine gas system may have over-gassed it.

ETA: Take a look at your trigger spring too. One leg of the trigger spring (on the same side as the magazine release button) looks bent as if it's going upwards. Both trigger spring legs should be under slight spring pressure pushing down on the fire control pocket floor. -CB

Umm looks correct to me.  And yes it's mid length.  You just called it carbine length so I was trying to bring light to that.

Okay. The hammer spring looks good to you. Unfortunately, it is installed backwards. Might I also kindly suggest you promptly pay a visit to your optometrist? As stated in my post above, the trigger spring looks suspect as well. And I also think it's possible your Magpul MBUS sights are counterfeit copy's not fit for use on firearms. Take it for what it's worth, free advice it didn't cost you anything. Still a nice build. Have a great day. -CB

You may be interested to know there is a thread on this form specifically dedicated to listing lightweight parts and their actual weights as measured by users:
Lightweight Parts List with WEIGHTS

car·bine
noun
a light automatic rifle.
historical
- a short rifle or musket used by cavalry.

He was referring to the actual rifle, not your gas length.

Your hammer spring is definitely on backwards


Also just FYI in case you didn't know, the way overall barrel length is measured is from the face of the bolt when it's in battery, so the barrel extension is not included in that.

For those looking to build lightweight carbines, Faxon has the pencil and gunner barrels 20% off during the NRA show.
Put it in your cart and you'll see that a 16" pencil barrel is only $140. (shipping for me was $8 for 2-day shipping)