Building the lightest AR10 ever

[breastroker]

I agree with these facts:
Here are the places modern AR10's are porky:
Heavy Barrels
Massive Carriers
Unnecessarily beefy receivers
Rail with scope is heavier than integral carry handle.
Forward assist adds weight.
Handguards and stocks are not as light as the fiberglass originals

I have been building light weight AR 308s (AR 10 is Armalite) for several years now. My first AR 308 was a DPMS Long Range Hunter, about 9.5 pounds without scope.

My first light weight AR 308 ended up at 5.99 pounds using a Faxon 18 inch midweight barrel.

After that the next one came in at 4.8 pounds using the new (2/2016) 2A receiver set and a sweet fluted Juggernaught 18 inch 5R barrel that weighed just 36 ounces. Soon I replaced that barrel with an 16 inch X-Caliber barrel that weighed 31.3 ounces. Also got the first titanium carrier so my BCG was down to 18 ounces from over 23 ounces.

Now I am waiting on a lightweight Faxon 16 inch 308 that weighs 28.64 ounces. Not made for shooting 300 rounds a day, hoping to get 3-5 shots under 1 MOA before the group opens up.

I have my lower down to 16.35 ounces complete, and the upper parts without barrel adds up to 27.20 ounces. So the upper will weigh 55.85 ounces. Total weight will be very close to 4.5 pounds. I have been shooting under 6 pound AR 308s for a couple years now, so I know the ins and outs of recoil reduction.

Now everyone is going to say the recoil will be brutal. NOPE, just a mild push.
I have a VERY BAD shooting shoulder (right) so bad many nights I have to take 2 naproxen. So days it is excruciating just to raise the arm to shoulder level.

The secret to a mild AR 308 is lightweight reciprocating parts and a good adjustable gas block, and a good muzzle brake.
My total reciprocating weight is 21 3 ounces, BCG + buffer. Those who have actually shot an AR 10 or AR 308 will say the rifle has a sledge hammer versus an AR 15 ball peen.

But the absolute need on any AR 308 is that adjustable gas block.

I can shoot maybe 10 rounds of 147 grain without a muzzle brake. Again less than 20 rounds without a adjustable gas block.

When I shoot my 308s I typically bring 2 to 3 boxes of 175 SMKs for each rifle, and sometimes I shoot the 130 SOST ammo, just a fun round. So usually 100 to 160 rounds at the range without any shoulder problems.

 

[badkarmamib]

Got any pics? Estimates of costs to build? I know the featherweight trend of AR15s was really big not too long ago. Sounds like you had fun with this project.

 

[Jackal]

The DPMS GII AP4 is easy to get into the low 6lb range using the factory barrel.

 

[breastroker]

Six pounds is heavy and the DPMS GII is expensive. Pretty sure I can build a 5.0 pound AR 308 for the price of the DPMS GII.

 

[breastroker]

Ten minutes ago I got my new Faxon Barrel 16 inch 308 pencil profile weighing in LESS than what was listed @ 28.35 ounces. I needed that to weigh less in order to meet my goal of 4.5 pounds.

2A Xanthos receivers with Faxon 16” pencil barrel

Early in March 2016 I built my Ultralite AR 308 using 2A Xanthos receiver set and are-profiled X-Caliber 16” 308 barrel. Upper weighed 58.2 ounces and lower 18.70ounces for a total weight of 77 ounces or 4.8 pounds. That is 5 ounces morethan my stated goal of 72 ounces or 4.5 pounds.
April 2017 Faxon finally came out with a pencil profile16 inch 308 barrel that weighs only 28.64 ounces.
The goal is 4.5 pounds using DPMS Gen 1 AR 308 pattern parts. (72 ounces)

My last AR308 got down to 4.70 pounds by 11/5/2016 with the X-Caliber-profiled 16” barrel.

Below is with the new Faxon barrel.

Upper Parts: Total weight 55.40 ounces

2A Armament Xanthos Upper receiver 7075 T6 @ 9.00 ounces
Faxon 16” pencil profile 308 barrel @ 28.35 ounces
Tactical Intent adjustable titanium gas block @ 0.45 ounces
Gas tube mid length @ 0.80 ounces
titanium muzzle brake @ 0.60 ounces
Clark Custom Aluminum barrel nut @ 1.18 ounces
AR 308 carbon fiber hand guard 1.60 ounces in mid length 10.5 inches
Toolcraft Titanium 308 BCG @ 11.80 ounces with ti firing pin
Vltor charging handle @ 1.25 ounces


Lower Parts: Total weight 16.35 ounces with polymer trigger

2A Armament Xanthos lower @ 7.30 ounces
Mag Pul K grip @ 1.50 ounces (41 grams)
V7 titanium grip screw 0.113 ounces
V7 Mag catch aluminum 0.173 ounces
New Frontier polymer selector 0.1 ounces
V7 aluminum AR 308 takedown pins 0.26 ounces
V7 tool steel bolt catch 0.299 ounces
Smoke Composite stock 3.3 oz.
AR15 carbine buffer (no weights) 0.85 oz.
(Topcom polymer buffers 0.70ounces)
NF polymer trigger group 0.65 ozwith titanium trigger pins
DPMS carbine buffer spring @ 1.4 ounces
Titanium buffer retainer, mag catch plunger

Total rifle weight withoutscope is 71.75 ounces or 4.48 pounds


Also my official sight will be the Vortex Venom @ 1.1 ounces.

 

[breastroker]

Here @ 71.80 ounces

 

[hdwhit]

breastroker wrote:
So days it is excruciating just to raise the arm to shoulder level.

Have you been to a doctor? Have you been diagnosed with "Adhesive Capsulitis" (a/k/a Frozen Shoulder)? If so, have you been referred for physical therapy? My wife has had it twice in the last dozen years and each time, some fairly aggressive physical therapy combined with what the place called "hard massage" therapy restored her range of motion in about six months.

 

[hdwhit]

breastroker wrote:
Total rifle weight without scope is 71.75 ounces or 4.48 pounds

Fascinating.

What has me really curious is how you deal with managing the recoil impulse.

If I'm asking you to reveal a trade secret, just tell me to mind my own business and no offense will be taken.

But do you do it through a combination of moderating the amount of gas bled from the barrel so as to control how fast the bolt carrier starts to move combined with a particular weight buffer and carefully selected recoil spring? Or have I totally missed the boat and you're doing it some other way?

Gee. Suddenly I'm starting to want an AR308.

Good job.

 

[breastroker]

Recoil control is through lightening the reciprocating mass, the muzzle brake and the adjustable gas block.

 

[Speedo66]

Since less is more, lightness costs money. Can you give us a ballpark figure on what it costs to assemble a feather light build like that?

 

[breastroker]

The major parts costs are:

Faxon barrel $259
2A receiver set $660
Toolcraft Ti BCG $450
Smoke Composite Stock $189
SSA-E trigger $220

NOTE: All of these parts were bought on sale with between 10% and 25% off. So if you have served, are a LEO or first responder your costs will be much less. Or buy during sales like 4th of July, Labor Day or Thanksgiving, that is what I do. For instance the SSA-E trigger was just on sale during Memorial Day for $180. Got the Faxon barrel for $194 and the receiver set for $594.

 

[breastroker]

 

[Speedo66]

Thanks for the price info, I had a feeling it would run around $1600 more or less.

 

[salt&battery]

it seems like a 308 that light would only be good for hunting. amazing how light it is

 

[1stmarine]

Hi mang! .. Nice to see you here on this side of the Mississippi.
Love this "Gen 3" rifle you are building.
Be careful with the wind gusts so you don't loose it.

 

[breastroker]

Shot today needed less than 20 rounds to get OK for further testing. Gas block adjusted from DAM to mild recoil. Shooting at 91 degrees wind less than 10 MPH from 90 degrees. Using 130 SOST ammo, last two shots the bolt held open finally.

You aren't far from the truth here in Lost Wages, many times the range closes when wind over 25 MPH, we had 60-80 MPH winds in March that blew down trees 60-100 years old.

 

[breastroker]

It would be good for a bug out gun, lot more stopping power and you could load up with a couple hundred 308 ammo. With this great Leupold AR 18 power scope mil dot (18 ounces with mount) I should be able to ring steel at 300 and 400 yards all day.

This would be a great hunting gun for the Rockies or for hogs anywhere.

The very first shot today I held strait out far from body just in case, like DAM kicked like a mule. Immediately shout down gas and then gradually opened back up SLOWLY. The 130 SOST Mark 319 ammo is hot, over 3000 fps in a longer barrel.

The buffer spring is too powerful, going to replace with a couple of weaker ones next trip and try the Federal Premium Gold 175 SMKs should give half inch groups at 100 yards if the 130 group is any indication. Only going to shoot 3 or 5 shot groups until the barrel is shooting it's best, usually after 60-80 rounds even with QPQ coating.

Eventually will try a mil spec 147 grain NATO round 3 shot group, followed up be a 10 shot rapid fire to see how much the group spreads out with this pencil barrel.

 

[Zerodefect]

I'll second the DPMS genII. If any of them work yet.