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imschur

Build a Light Weight 308 AR

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From the components I recall, I think it's going to be hard to beat the build Robocop's doing, unless you were to do an all out competition build with low mass carrier, Ace stock, carbon FF tube and pencil barrel, and then probably not by much.

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My build:

*SI-Defense Gen 3 "Fail Zero" Upper

*SI-Defense Lower (Drk OD)

*Apex CNC 12.5 handguard (Cerakote-Olive Drab) with full length Apex CNC top rail and 2" polymer side rails

*Mike Rock / ABS (carbon wrapped) 17" Barrel - Still on order as of 04/2011

*SI Defense Stainless Steel "Fail Zero" Barrel Extension - Shipment Pending 12/2011

*SI Defense Stainless Steel "Fail Zero" Carrier - Still on order as of 04/2011

*SI Defense Shot-Peened "Fail Zero" Bolt - Shipment Pending 12/2011

*SI Defense Stainless Steel Bolt Catch

*BCM "Gunfighter" Mod3 Charging Handle

*Chip McCormick Flat Tactical Trigger (3.5 lbs)

*BAD, Inc. 45 Degree Ambi Selector Switch (Stainless)

*PRI Upper Height Railed Gas Block (Rifle Length Gas System)

*Magpul MIAD Pistol Grip (OD)

*Ace ARFX Skeleton Stock (Cerakote-Olive Drab)

*Magpul AFG2 (OD)

*Tubb CS Flat Buffer Spring

*Enidine "AR-Restor" Hydraulic Buffer

*Magpul MBUS (OD) with Trijicon front sight post

*VLTOR Side Mounted Mod-Pod

*Battlecomp Stainless BABC

*Magpul LR-20 Magazine (Cerakote-Olive Drab)

I could have gone lighter, as Jgun stated, but I wanted to keep the tactical features of the rifle as well as the sub-MOA... all on top of the lightweight frame. My intention was to build a rifle directed at LE purposes. Any lighter and I would have had to compromise integrity and reliability.

In the end, my rifle should shoot sub.5 MOA, pop like a .223, and only weigh around 7 to 7.5 lbs.

IMG_1601.jpg

(The length of that list should be a hint to what this has all cost me so far.)

Eventually, I plan to mount a scope soon too. The 2-10x32 NF and the 2-12x36 IOR is the debate. Maybe an off-set micro red dot too. Finding a lightweight mount is an issue too.

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I have had an interest in this topic for a long time.  I want something at/below 7lbs to make it a more handy woods rifle.  My nekkid DPMS AP4 weighs 8lbs 2oz, no iron sights, no magazine.  I have been told the 16.5 inch barrel weighs 2lbs 7 oz and /i am hoping to get it turned down under 2lbs w/o chopping it further.  This rifle will be well maintained but double as a hunting stick when need be or a plinker out to 500-600 yards.  I will not go with a CF barrel, but just ordered a CF handguard.  I want this project to work  <thumbsup>

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I've weighed several .308 AR receiver sets, all billet, I have not had an opportunity to weigh a forged set. All of the sets that I've weighed have been within 7 oz of each other, with the Kaiser set being the lightest, so, although you can save some weight there, I don't think it's going to be as significant as in other areas, besides which, people seem to favor a particular receiver due to esthetic's or brand loyalty anyway,  I think that in the AR platform the three places that you have the ability to make the difference between a "heavy" gun and "light", is the barrel, handguard, and stock. Of course, everything is going to be a trade off. In my experience the CF barrel is not going to be any lighter than a pencil barrel but will give better accuracy. I have not had mine long enough to comment on any extended lifespan,(will probably take me years). In most cases, I don't think the additional cost of the CF barrel is justified. You can save at least a pound on a handguard going from a cf tube with nothing nounted, to a full length railed handguard (with nothing mounted). Same for the stock, A Magpul PRS or Ace Hammer stock will weigh 1.5 lbs more( I think) than the fixed Ace stock. Of course, none of this takes into account the weight added when you mount an optic (probably at least 2 lbs with quick release mount) or any other accessories you might feel the need to mount, and a full mag of 308 isn't exactly light, so, although I'd say you can build a mid 7lb .308 AR, it won't be that weight when your carrying it in the woods, unless it's empty and your using BUIS exclusively. I also realize that all of the accessories will add the same additional amount to a 7lb gun as they do to a 9lb gun so weight savings is weight saving regardless.  One thing I have found is that the smaller mass of the small platform AR's is beneficial in quick handling of the gun. My 300BLK is a much better handling gun with a TR 24 mounted than my CF barreled Kaiser .308 is with BUIS, and the 300  with optic mounted weighs more than the .308 without. Of course, the Blackout is only good to 300yds, so if you want/need the range/power of .308, it comes at the price of added weight/bulk. I'm looking forward to hearing just how light you guys can build these .308's as well, and I'm also going to be interested to hear how much they end up REALLY weighing as configured with all of the accessories you mount on them.

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Weight breakdown for a DPMS AP4 16.5 M203 notched barrel and gear.

2012-01-02_11-49-01_314.jpg

.308 DPMS AP4, no iron/optical sights, no magazine = 8lbs 2.3 oz
Upper Receiver (total) = 5lbs 12.4 oz
Lower Receiver (total) = 2lbs 5.9 oz

Components:
Lower Receiver (no buffer, spring, or stock) = 1lb 8.3 oz
Buffer = 3.8 oz
Buffer + Spring = 5.3 oz
M4 Styled stock (collapsing) = 8.3 oz (7.3 if you remove sling swivel)
Magpul CTR stock (collapsing) = 9.0 oz
CAR15/XM177 Stock = 4.4 oz

Upper Receiver (no bolt/charging handle) = 4lb 8.2 oz
Bolt Group = 1lb 3 oz
Charge Handle = 1.3 oz
Flash Hider/Washer= 2.4 oz
Gas Block (no sight) = 3.1 oz (includes gas tube)
Barrel (No FH)= 2lb 7.7 oz
Handguard = 10.4 oz
Upper Receiver (no bolt, with FA & DC) = 1lb .5 oz
Sights:
Millet DMS 1-4x24 + heavy duty mount (w/o flip covers)= 1lb 8.8 oz
Leatherwood Hilux 2-7x32 with quick throw rings= 14.9 oz
Aimpoint T-1 and high rise mount=5.8 oz

Magazine/Ammo
1 Round of .308 168 grain match = .9 oz
Empty 20 round P Mag = 5.7 oz
20 round P Mag w/5 rounds of .308 168 grain = 10.2 oz
20 round P Mag w/20 rounds of .308 grain = 1lb 7.8 oz
5 round P Mag (20 cut in half)= 3.7 oz
5 round P Mag w/5 rounds of 168 grain= 8.3 oz

This is just to put that info out there, so you can compare where you might find some weight savings.

Edited by Glockslap

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Just ordered the JP light bolt and adjustable gas block.  I will weigh them as soon as they come in.  Indications show a potential loss off 5+ oz from the bolt group alone.  Don't know if there will be gas block savings ( Ihope so) yet.

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Looks like a maximum weight loss of 4.5 oz with the bolt carrier alone.  As promised, here they are (sorry about the not so great pics):

2012-01-10_18-56-57_101.jpg
VS:


Side by side:
2012-01-10_19-02-43_346.jpg

Here with the DPMS bolt, total weight:
2012-01-10_19-07-33_966.jpg

Adjustable gas block:

2012-01-10_18-52-39_724.jpg

Edited by Glockslap

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Just updated the weight on a CAR15/XM177 "old school" collapsing stock and weighting on the CF handguard, which should hopefully be here tomorrow.  Also spoke with SI Defense (NEMO) and trying to get a Gen 3/4 upper exact weight loss compared to my stock DPMS upper.

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Just received the carbon fiber carbine handguard and barrel nut-sucker feels WAY lighter then the scale's indicated 3.2 oz, and with the supplied barrel nut at 1.7, manages a rounded up total 5 oz when weighed together.  Now to just find out how much the stock AP4 aluminum handguard+ barrel nut...I'm really hoping for at least another 4+ oz or more to save me a chunk of weight.

Also waiting on SI Defense's Gen 4 upper which I hope will check in at 13 oz or less, and should hopefully shave another 3-4 oz off the stock DPMS upper receiver.  Further, just ordered a short 5 round PMAG to help lighten the load for hunting (and stay legal).

Edited by Glockslap

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Added 5 round P Mag weight.  This weekend I will have the AP4 upper broken down to be able determine exact barrel, handguard, and upper receiver weights.  It should let me know if under 7lbs is achievable w/o going to radical.

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Did you manage to weigh the AP4 barrel?

I have a Fulton Criterion 18.5" lightweight barrel, but hesitate to tear my AP4 upper apart unless it will be s significant weight savings.  I would also swap out the DPMS quad rail for a Troy TRX.

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Upper Receiver Broke Down!  Happy to find the carbon fiber handguard is saving me over 7 oz alone  8)

Unfortunately, no weight savings with the DPMS gas block vs. the adjust one  :P

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Ok, so what does the AP4 barrel weigh?

Will post a few weights as I re-do my rifle.  Really curious how much the DPMS quad rail is, looks like an awful lot of excess aluminum in the thing, compared to the Troy.

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Sorry-forgot to mention in my post the changes to my weight post.  Forgot this was not my original thread!  The barrel is 2lbs 7.7 oz (below):

Upper Receiver (no bolt/charging handle) = 4lb 8.2 oz
Bolt Group = 1lb 3 oz
Charge Handle = 1.3 oz
Flash Hider/Washer= 2.4 oz
Gas Block (no sight) = 3.1 oz (includes gas tube)
Barrel (No FH)= 2lb 7.7 oz
Handguard = 10.4 oz
Upper Receiver (no bolt, with FA & DC) = 1lb .5 oz
 

Edited by Glockslap

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The barrel is 2lbs 7.7 oz

Aw hell, that is only ounces more than the Criterion 18.5" CL lightweight.  Was hoping the AP4 would be around 3lbs, and make it worthwhile to tear things down and swap it. 

Maybe just shoot the 16" out and save the longer barrel or build another upper.

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After reading your post, just out of curiosity, I weighed some parts I had laying around here. I weighed a POF lower (12oz), a butt stock with buffer tube , not the lightest (1lb 4 oz), and a grip, light weight buffer and spring (10 oz). I don't have a trigger to weigh but from the looks of it, it sounds like you may end up with a gun weighing in at around 7 1/2 lbs, without optic,. That will certainly be one lightweight .308 AR. 

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For more reference, a few weights.  The ACE skeleton is said to be a lightweight alternative to the A2 stock, and it may be.  But, it is heavier, with rifle tube, spring, and buffer, than an AP4 carbine stock, with RE, spring and buffer:

ACE/rifle tube/spring/buffer    1lb 5.9oz

AP4/spring/buffer                  1lb 3.1oz

My Upper with DPMS quad rail and all guts in place,  16" AP4 barrel, DD rail mount sling attachment and rail covers still on.  Gas block is a JP A2 sight adjustable:

Upper with 16" BBL/quad rail  6lb 2.56oz

The JP A2 GB is spec'd at about 4oz, a railed GB I have on hand is 2.6oz.

For me at least, any significant weight change will be going to the Troy TRX handguard.  It weighs 13oz with nut.  Considering I am going to a rifle length barrel and HG, looks like it will still be lighter than the carbine setup.

A Miculek compensator I have is 4.1ox, an A2 flash hider is 1.0oz, both with lock nut or washer.

Playing around in a spreadsheet with all this, but for me, looks like it comes down to how much weight comes off with the DPMS quad rail.  No huge areas of excess to be removed as Glockslap has already shown.  Great fun regardless if you are mechanically inclined...........

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The numbers should be closer to 7lbs, since I am sure I can get 5oz off of the barrel, and now that you mention the A2 being lighter, another oz off from the FH.  The key will hopefully be saving an extra few ounces from the NEMO upper receiver, but I can't seem to get in contact with them.

Every ounce counts in this one  <munch>

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I am waiting on the NEMO's Gen 4 upper, which should be here in *hopefully* less than 2 months.  It is supposedly 3 oz lighter than my current DPMS upper.  I am not sure if I will send off the barrel for contouring earlier, or ship it all together.  I'm also going to add and A2 FH, which should also save me 1 ounce.

So far, I'm -3oz for the upper reciever, -4 oz for the bolt, -7 oz for the CF handguard, -5 (potentially) for the barrel, -1 for the A2 FH (potentially), and -4 for the XM177 styled stock.

Once all put together, I will have an exact weight.  After checking for function at the range, I will have to try to find the lightest sights possible as well.

If my math is working out, I'm at 6 lbs 14oz with current AP4 collaping stock, and 6 lbs 10 oz with XM177 styled stock (which might be pretty harsh in .308 due to it's reduced surface area; I may try to increase the surface/and or add a superlight recoil pad)

Edited by Glockslap

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