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Building an AR-308. Follow the build:

This is a discussion on Building an AR-308. Follow the build: within the Hobbies and Special Interest forums, Tweet I do firearms. Lately, I have been building up for rifle Gas Class competitions. Generally, our club is dedicated ...

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    fixxer's Avatar
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    Building an AR-308. Follow the build:



    I do firearms. Lately, I have been building up for rifle Gas Class competitions. Generally, our club is dedicated to bench-rest shooting. I find shooting off a reciprocating rest at the same distance every time just plane boring... We finally voted in a Gas action class that will run 25, 100, 200 and possibly 300 and 600 yards soon. I am going to document the 308 AR build that I have started from the ground up. This is a hybrid between an SR25 and an AR10 that I intend to shoot off a bipod only.

    I have been accumulating parts since 2012. Momentum really picked up once I finally found a hybrid SR25/LR308/AR10 billet upper/lower receiver matched set that fit my wants.

    This build is going to be an attempt to build a middle weight, reliable, Match worthy auto loading rifle using no more or no less than the required specs, effort and $ to get there. There will be no CQB/mall ninja gadgets bolted to this platform. Think of this as a "sleeper" rifle. It will look a lot like a practical hunting flat top AR with no quad rails, flashlights, grenade launcher mounts, bayonets, LASERS, etc.


    Here is the build sheet. All major parts are on hand (receiver set, barrel, optics etc).


    Some small parts are still on order and due to arrive by early May, 2013.
    Upper Receiver Group


    Kies KR-10 GenII billet matched upper/lower set from Joebobs Outfitters.



    Rainier Arms 20" 308 Ultra Match barrel with LR-308 extension. This is a proprietary cut profile that runs .750 at the gas block. It weighs only .8 more lbs than a light weight barrel. I intend to have the barrel Cerakoted to match the rifle once it proves itself.



    PWS 5/8X24 FSC30 Muzzle brake/flash hider combo.



    Troy Industries TRX Extreme Battle Rail Modular Free Float Handguard (DPMS LR-308 with Low Profile Upper Receiver) Rifle Length.



    Dewey Stainless Rifle Length Gas tube. I will have this Cerakoted also.



    Troy Industries Low Profile Gas Block
    Syrac Ordnance adjustable, locking clamp style gas block (clamping style not shown).


    DPMS Gas Tube Roll Pin



    Leo Armory custom laser engraved 308 dust cover. "Calico Jack" and "Send it" engraved on the inside of the cover. That's just fun.


    DPMS Ejection Port Cover Pin for 308



    DPMS Ejection Port Cover Spring



    DPMS Ejection Door Snap Ring



    Black Rain Ordnance Nickel Boron BCG.



    DPMS Forward Assist (AR15 kit + LR308 style spring). This will be mostly cosmetic as most 308 BCG's are not cut with pawls. It will still push on the carrier from behind when it is "nearly" in battery. That is all I wanted...



    Rainier Arms Raptor Ambi charging handle for 7.62 rifles.





    Lower Reciever Group


    DPMS LR-308 Lower Receiver Parts Kit (I don't like their LRPK's but I am only using a few parts out of it). The trigger group is being replaced altogether with the SR-Gold trigger.



    Pact ATC SR-Gold trigger.



    J.P. Enterprises Silent Captive Buffer and Spring for AR-308.

    Lower Receiver Extension Tube (Fixed A1 style).



    Magpul Moe Fixed A2 Stock (Black).
    I still have no idea if this is going to include the buttstock screw. Some say it does. I dunno. Magpul makes no mention of it.





    Optics:
    Trijicon 2.5-10x56 Accu-Point, Green Triangle Recticle (TR22G) from my last rifle.


    I might swap out my Vortex Viper PST 4-16 X 50 (Front Focal Plane, MOA Reticle and Turrets).
    I'm considering a new mid-range fixed power scope with a smaller Objective as well. I really think I can live with fixed power. For now, I'll commission it with what I have and see if I can get the scope low enough without cheek weld risers.


    Burris Xtreme Tactical Rings. I use these for every application lately.



    Tools I did not have for AR-308 finishing.
    Had to add the following to my tool load out for this project. I don't know if I consider these parts directly part of the project expenses. My tools generally have their own budget and are more valued than "parts". Hopefully, I will get more use than this one project out of them:


    Wheeler Engineering Delta Series Upper Receiver & Picatinny Rail Vise Block AR-15, AR-10, LR-308



    Clymer Go/No Go Headspace Gauge Set.



    I have had Pmag 5 pack on order for this build from Brownell's since December. I haven't seen any update on these other than they are shipping some regular Pmags I ordered right after the crazy hit the market. 5 of those 5.56 Gen 3 mags are on their way. That doesn't help me a lot here... I ordered (2) steel DPMS 308 20round mags that were in stock to get me by.


    Once all parts are completely in hand, I will start assembly and post pics of the progress.
    Last edited by fixxer; 04-29-2013 at 07:27 PM. Reason: Updated
    2012 Tundra Crewmax Limited 5.7L loaded with Sunroof, JBL Nav/Entertainment, OEM matching tonneau and OEM brushed running boards.
    First mod: Putting the Hula girl on the dash.


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    TRD Duckslayer's Avatar
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    That will be one sweet rifle when its done. I would love to build on like that, but i just spent 3k building a 5.56 ar. So i won't be building one for a long time.

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    TRD Duckslayer's Avatar
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    That is a sweet barrel.

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    Toxarch's Avatar
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    Looks like a pretty nice list. With that barrel, I would definitely go with a adjustable low pro stainless gas block. Develop a reload and then fine tune the gas system. The bad part about the adjustable gas blacks is the adjustment screw can back out over time. Some people use a thread locker, some dimple the metal next to the screw. I would also put a different grip on the rifle for comfort.

    Look on Ebay for BTE (Battle Tested Equipment) gas blocks. They are 100% made in the USA, come in great condition, and are about the same price as the one you are already planning ($50 shipped) for a stainless adjustable gas block.
    Any questions about truck mods I have done need to be asked in the forums. Don't send me a private message about mods cause I probably won't answer that PM unless there is money involved.

    2007 SR5 Crewmax 5.7L 4x4
    Mods: nerf bars, Truxedo tonneau, radar detector power, 3M clear bra, fog lights, black billet grille, rear differential breather, parking sensors, Line-X, power tailgate lock, hood safety latch mod, one off driving lights behind grille, Pioneer NAV w/ OEM camera, CDT 6.5" speakers, Flowmaster 50 SUV dual/dual, blue LED dash lights, Volant CAI, Llumar tint, CompuStar Pro alarm, ProComp 6066 20" wheels, Nitto Terra Grapplers LT305/55/20, OME HD coilover lift, Firestone helper air bags, 55w reverse lights, stereo cable lock, Tekonsha P3 brake controller, colormatched exterior parts (de-chromed truck), Weathertech floor mats, eDead sound proofing, CDT Audio speakers, Custom made speaker brackets, LED foot well lights, PRG/Deaver 3 leaf mini-pack, LED map lights, Air Lift WirelessAir system, Bed LED Lights
    All mod descriptions and pictures 2007-2014 by Toxarch. They may be copied only for personal use and the mods may be done for non-profit only.

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    Arhino04 is offline New Breed
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    I run that buffer in my .223 I built and love it im sure the .308 version is just as awesome. Also let me know how you like the trigger and have you used that one before?

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    Awesome project! If things settle down again I think an AR-10 is in my future.

    2015.5 GMC Sierra 2500HD SLT All Terrain
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    Mods- WeatherTech front and rear floor liners, 20% window tint on front doors.



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    fixxer's Avatar
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    Thanks guys. Here is a little background, since I am still waiting on parts. And maybe some of your folks are actually interested??? I hope so, because I do not do well as a Tundra Mechanic. And I am putting a butt-ton of money into this... LOL (seriously, between this and the optics, I could be at least 1/2 way into a supercharger kit if I had a non-Ethenol ready engine ). I did not "copy" this from forum burners. This is my own experience here; if I am wrong, then I have no one else to blame. In most cases, I have gone directly to the specs and looked at them millimeter per millimeter, test for test.

    Please don't feel like I am talking "down" to you if you already know this. I was only learning this about 1 year ago when I started getting serious about an "AR10" build. I had thrown together other AR15's and thought "what's the big deal?" before I started doing a lot of searching. That led to more findings until all the little nuances in the specs I was planning started to make sense.

    Some folks might think that these are just more boring AR builds. Which, they can be similar to. But the difference between AR 308 building and AR15 building is night and day.

    While it is true that some parts are cross compatible with an AR15, there are also many fundamentally different design differences that can cost you a fortune if not planned correctly. For example, AR10 is an Armalite branded propriatary model that cannot use the same magazines that Magpul sells in 308 form. That is because the magazine well is too long to allow a curved magazines to fit. I also understand that the follower will not hold the bolt open on the non-curved, lower capacity mags. So, there is a big discrepancy by calling any AR 308 an "AR10". Calling all AR 308's an AR10 is as ignorant as calling all 1/2 ton pickups "Fords". Just like "magazines" or "mags" are not "clips". If you want a generic term every builder will understand, then that would be "AR 308" or "308 AR". And many parts of the AR10 are not compatible with other makes of AR 308 designs. This is just to help avoid confusion of terms that might be interchanged.

    There is also a matter of upper and lower receivers being proprietary. There is no such thing as a completely Mil-Spec Lower receiver that accepts all other "Mil-Spec" 308 upper receivers on the market. Rock River Arms; for example, cannot use anything but RRA. The DPMS LR308 upper cannot be mated to an Armalite AR10 or Fulton Armory "FAR-10" lower, so on and so forth. And when it comes to companies selling upper receivers, there is sometimes a large disparity between their own models.

    For example, DPMS makes upper receiver variants that fit their own lower, but have different profile height picatinny rails. If you are not careful, you can buy the wrong profile free float rail and end up screwed with a 1/8th inch or so mis-match in picatinny height... That would suck. There are 4 major profile height differences. Optics rails (extra high), Armalite rails, DPMS high profile rails and DPMS Low Profile rails. Low profile is the flavor of the week right now. I do not recall seeing a 308 upper with integrated carry handle (A2 style). I'm sure someone makes one of those too; but I suspect you will need to buy their proprietary lower to fit it to.

    Bolt Carrier Groups: The biggest headache I had was researching the bolt compatibility between the various rifles. I wanted a nicer bolt that was unobtainable directly from DPMS. I kept reading "only use AR10 BCG's with Armalite barrels" and "you can use any 308 BCG with any AR 308 barrel" etc. This was a major headache to sort out since I cannot exaclty drop into a gun shop in my locality and ask to tear down their rifles (believe me, I thought about it but there were none to be had together). But the end solution is very simple.

    I finally came across the data of the Bolts and complete BCG's together: What you cannot do is mix DPMS, Armalite, or RRA bolt carrier groups together. It has nothing to do with the headspacing or the barrels. All bolts are in fact cut to the same depth. (I am guessing Armalite's spec was ripped off since their rifle was the first.) You cannot mix carriers and bolts between manufacturers. DPMS bolts and Armalite carriers do not fit together. This is because they do not attach to the carrier the same and the firing pins inside the BCG are different.

    Firing Pins: The firing pins are unique too. Armalite AR10 uses a spring return firing pin system that others do not. So the bottom line is you can use the entire group with either barrel. You can; in fact, use Armalite bolt carrier groups in DPMS barrels and vice-versa.

    Head spacing: There is a lot of confusion about AR "headspacing" and differences between an Armalite pattern and LR308/SR25 pattern rifle. To be honest, you can throw an Armalite barrel in a DPMS upper and let it rip. And as mentioned, there are not problems between bolts fitting them. Provided you keep the barrel screws with the upper receiver.

    Barrel Nuts: DPMS and Armalite use different barrel nut thread patterns for the upper receiver to hold the barrel in place. The other only difference is in the bolt and carrier as previously mentioned.

    Head space and "kaboom": The deal is, you cannot tap the gas port until you install the barrel extension. Unless you are buying blanks and machining them, this is done at the factory that makes the barrel. Otherwise it would mean that you are "guessing" the orientation of the gas port (which must be set to 12' O-Clock relative to the barrel extension). Once the barrel extension if either barrel is set to 308/7.62 NATO specs, the gas port is drilled relative to the barrel extension. That is why AR's are so simple to assemble.

    While it is recommended that you do check your head space with a set of "Go/No-Go" gauges, there is nothing you can do to fix a barrel that is not head spaced correctly. It is time to send it back to the manufacturer to start over again. That also means if you supply a worn bolt to Kreiger to build your barrel (or whoever), you better be content in living with that bolt for the rest of your barrel's life. (Unless you are willing to hand-fit and machine plane another). The same goes for AR15's. Don't supply used bolts to get a custom barrel machined. They are not that expensive. Look for "mil-spec" 308/7.62 Nato head spacing or go all in and buy a new bolt to match a new barrel with if you are paying to have one custom turned. Even the enhanced bolts are not too pricey.

    Besides, if you are paying the $$$ to have Bartlein, Kreiger, Obermyer etc. cut you a barrel, that little bolt you have to supply to them is the least costly concern you have. You don't need a whole new BCG, just the bolt.

    Also, once a bolt is broke-in or worn into a particular action, it is best to keep that bolt with the barrel. You are going to screw yourself in terms of accuracy if you keep swapping bolts around in your rifles. The same is true for gas actions as it is for bolt actions. Would you swap your 30-06 bolts around? Nah, probably not.

    Gas tubes: Gas tubes for Armalite AR10's are a different animal. The length is slightly different. One of the reasons I went with the DPMS LR308 style route is for more AR15 compatibility. LR308 gas tubes are identical to AR15 specs. This makes things easy.

    Buffers: 308 Buffers are pretty much 308 buffers. Some folks have been using heavy AR15 buffers. They are bottoming out the buffer spring unless they are running an adjustable gas block and actually tuning the rifle. There are some really good products out there. I do not recommend throwing the "carbine" buffer in your rifle that came with your M4 style butt stock kit. AR 308 bolt carrier groups are much more massive than AR15's are built to tolerate. There are varying weights of buffers. The rule of thumb is that heavier mass requires heavier buffering.

    Adjustable gas systems: These are the cats meow if you are planning on changing things up. They are also necessary if you are planning on suppressing your direct impingement rifle. Or if you plan on running a large change in ammunition weights. For example, you might come across a great "deal" on 155 grain ammo and buy the whole ammo lot after you set your rifle up to shoot 185 gr match loads. Keeping your gas block tuned to your action is a great way to extend the life of your rifle too.

    You can also change up the buffer system. Or you can go straight to gas-piston systems. But be warned, gas piston systems also need tuned and should not be "over gassed" either. Gas piston is not the magical "end all" that some know-it-alls think it is. Some folks seem to think gas op rods are as easy to maintain as blow-back operation; and this is just not true. I have had all three and I honestly do not prefer one over all. There are always sacrifices to make when there are gains to be had. Armalite and DPMS gas tubes are not compatible to my understanding. Also, the barrel diameter is going to come into play here as well. If you have a 1 inch thick barrel you will need a gas block that accepts a 1 inch barrel. This is basic AR stuff. Again, DPMS accepts this part in AR15 specs. Another easy find for me.

    Well, that's it for now. I am trying not to let this die before I start the actual process of building. I am also not trying to kill you with data points. I was hoping that this is a decent primer for what we are about to start doing with this rifle during the build. I dig the comments; keep em' coming.
    Last edited by fixxer; 04-22-2013 at 02:07 PM.
    2012 Tundra Crewmax Limited 5.7L loaded with Sunroof, JBL Nav/Entertainment, OEM matching tonneau and OEM brushed running boards.
    First mod: Putting the Hula girl on the dash.

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    fixxer's Avatar
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    Thanks for the heads up!



    Quote Originally Posted by Toxarch View Post
    Looks like a pretty nice list. With that barrel, I would definitely go with a adjustable low pro stainless gas block. Develop a reload and then fine tune the gas system. The bad part about the adjustable gas blacks is the adjustment screw can back out over time. Some people use a thread locker, some dimple the metal next to the screw. I would also put a different grip on the rifle for comfort.
    Quote Originally Posted by Toxarch View Post

    Look on Ebay for BTE (Battle Tested Equipment) gas blocks. They are 100% made in the USA, come in great condition, and are about the same price as the one you are already planning ($50 shipped) for a stainless adjustable gas block.


    I had a hard time finding a .750 inch adjustable gas block. I figured I would start with a baseline and go from there. There is an adjustable gas block in this rifle's future. I just don't know when one will be available... I hope soon. I would like to re-assemble this rifle as few times as possible... I will follow up on that tunable gas block you mentioned. That sounds right up my alley. I can re-use this fixed one for a 7.62X39 barreled build I am planning. Ebay is out of everything but non-adjustable and micro aluminium.
    2012 Tundra Crewmax Limited 5.7L loaded with Sunroof, JBL Nav/Entertainment, OEM matching tonneau and OEM brushed running boards.
    First mod: Putting the Hula girl on the dash.

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    Toxarch's Avatar
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    Having never built an AR 308, I had no idea they weren't standardized and interchangeable. Thanks for sharing the info.
    Any questions about truck mods I have done need to be asked in the forums. Don't send me a private message about mods cause I probably won't answer that PM unless there is money involved.

    2007 SR5 Crewmax 5.7L 4x4
    Mods: nerf bars, Truxedo tonneau, radar detector power, 3M clear bra, fog lights, black billet grille, rear differential breather, parking sensors, Line-X, power tailgate lock, hood safety latch mod, one off driving lights behind grille, Pioneer NAV w/ OEM camera, CDT 6.5" speakers, Flowmaster 50 SUV dual/dual, blue LED dash lights, Volant CAI, Llumar tint, CompuStar Pro alarm, ProComp 6066 20" wheels, Nitto Terra Grapplers LT305/55/20, OME HD coilover lift, Firestone helper air bags, 55w reverse lights, stereo cable lock, Tekonsha P3 brake controller, colormatched exterior parts (de-chromed truck), Weathertech floor mats, eDead sound proofing, CDT Audio speakers, Custom made speaker brackets, LED foot well lights, PRG/Deaver 3 leaf mini-pack, LED map lights, Air Lift WirelessAir system, Bed LED Lights
    All mod descriptions and pictures 2007-2014 by Toxarch. They may be copied only for personal use and the mods may be done for non-profit only.

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    fixxer's Avatar
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    Small update. Changing gas blocks to an adjustable model. There is a very cool adjustable with locking detents from Syrac Ordnance. Push the button, adjust the screw, release the button and it locks into place. This is going to be used in lieu of the Troy non-adjustable that I ordered initially. I can use the Troy for another project. Or I can send it right back to Brownell's. They have awesome 100% returns and customer service. That is why I shop with them to begin with.

    2012 Tundra Crewmax Limited 5.7L loaded with Sunroof, JBL Nav/Entertainment, OEM matching tonneau and OEM brushed running boards.
    First mod: Putting the Hula girl on the dash.


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