LR-308 Build Help

Bocephus1776

Private
Minuteman
Nov 14, 2020
13
1
Missouri
Hi y'all. I'm building my dad a LR-308 and was wanting some advice. I've built about 10 AR-15's and a couple AR-9's but I know the large frame is a whole other beast. It's mostly going to be for fun and maybe some white tail hunting. Most shots 50-100 yards. We have a spot where we can reach 200 but it won't be something very often ( the property is a couple hours away). I'd like to build with the ability to reach 500 in case one of us gets some property. Here's what I've got

I have:
Lower = American Made Tactical
Upper = American Made Tactical DPMS low pro
BCG = Fail Zero Nickel Boron

Parts I'm looking at:
LPK = CMMG MK3 kit
Trigger = Rose Armament RA-434
Buffer group = KVP carbine tube with 5.6 oz buffer
Stock = MFT Battlelink (he has it on his 5.56 and wants it the same)
Gas Block = probably Faxon or Aero unless y'all recommend an adjustable

And now for the big question;
For the barrel I was looking at the Faxon 20" heavy fluted (p/n: 10B810R20FHQ-5R-NP3) or the Wilson Combat 20" Super Sniper fluted (p/n: TR-308SSRG20FT10) . Everywhere has been out of stock for at least 8 months. Should I wait until one of these comes available or is there another option for around $350?

Also, I'm going to build one for myself as well with pretty much all the same parts except I think I'm going with the PRS stock and I'm willing to spend between $500-600 for the barrel if the extra money is worth it. I was looking at the X-Caliber barrels but they seem to have mixed reviews on here.
 

hlee

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  • Jul 14, 2012
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    Here’s some unsolicited advice. Put all of your parts into a spreadsheet, with cost (including tax and shipping), and weight. A build can quickly spiral out of control on both of these fronts. Don’t forget rings, mounts, and glass. Nothing wrong with an expensive rifle, but you’ll likely spend more than you think you will. And, a heavy hunting rifle is one that gets passed up when it is time to go hunting...
     

    longshot2000

    Sniper's Hide Dealer: CHARLIE'S
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    Minuteman
  • Feb 19, 2017
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    charliescustomclones.com
    Best advice, save your parts for another day. Buy a full AR10 / SR25 / 308AR. The complexities of getting each part from a different manufacturer to fit and fit well and work in harmony is very hard in 7.62mm. Many would like to tell you that there are two standards, but that is just too far from true.

    And, you are going to give this to your Dad. Expect an active help desk. :rolleyes: .

    There are so many variables. If wanted to make it for yourself, then you would have yourself to answer to. When something does not fit when assembling, you have to go back to the drawing board and buy a new barrel or a new upper receiver or a new BCG. Those are the biggest fit areas. Let's say it all fits, and then has cycling issues. Is it the gas port, the gas block, the BCG, the spring, the magazine or the buffer weight? Maybe it is the ammo?
     

    rpoL98

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    Sep 27, 2017
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    definitely get an adjustable gas block. I use the SLR's but there are others.
    if you go with Faxon AR-308 barrels, you will need to use the Armalite AR-10 gas tubes, instead of the usual AR-15 gas tube.
    you might also consider Criterion barrels. when looking at barrels, be sure to pay attention to the barrel weight, some are pretty darn heavy. not saying to go with lightweights, the Faxon fluted match barrels are a step in the right direction, IMHO. and barrel availability is not great, right now.
    not sure about the KVP buffer setup, the 5.6oz weight sounds right, but you need to make sure it's a AR-308 buffer, and not an AR-15 buffer, they are different lengths.
    When selecting a handguard, you need to know if your upper receiver is DPMS-high, or DPMS-low, and pick the appropriate rail-height HG.
    Me personally, I would recommend a decent muzzle brake, for outdoors use.
     

    Bocephus1776

    Private
    Minuteman
    Nov 14, 2020
    13
    1
    Missouri
    definitely get an adjustable gas block. I use the SLR's but there are others.
    if you go with Faxon AR-308 barrels, you will need to use the Armalite AR-10 gas tubes, instead of the usual AR-15 gas tube.
    you might also consider Criterion barrels. when looking at barrels, be sure to pay attention to the barrel weight, some are pretty darn heavy. not saying to go with lightweights, the Faxon fluted match barrels are a step in the right direction, IMHO. and barrel availability is not great, right now.
    not sure about the KVP buffer setup, the 5.6oz weight sounds right, but you need to make sure it's a AR-308 buffer, and not an AR-15 buffer, they are different lengths.
    When selecting a handguard, you need to know if your upper receiver is DPMS-high, or DPMS-low, and pick the appropriate rail-height HG.
    Me personally, I would recommend a decent muzzle brake, for outdoors use.
    I'm definitely getting a muzzle brake. I was waiting to see which barrel that I went with first. Any recommendations? Good info about the Faxon barrel and Armalite gas tubes. I was not aware of that.
     

    Bocephus1776

    Private
    Minuteman
    Nov 14, 2020
    13
    1
    Missouri
    Thanks for the help fellas. I've told my dad a hundred times that home built 308's are finicky. He's just always wanted one and likes the idea of me building it for him. He's getting sentimental in his old age. I'll definitely go with an adjustable gas block now.
     

    rpoL98

    USA
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    Sep 27, 2017
    320
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    USA
    muzzle brakes: just my 2 cents ...
    for my 308's, I prefer the Precision Armament M4-72, or the VG6 Gamma when going cheap(er). for 6.5CM, I prefer the 6.5CM-specific VG6 Gamma 65. For TactiCool style, I've also used the Surefire SOCOM muzzle brakes, and the LANTAC Dragon.

    whatever tickles your fancy, there's a lot of selection out there.
     
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    mtrmn

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  • Oct 7, 2009
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    On the gas tube, make sure it comes out halfway of the cam pin cutout in the upper when installed-see attached pic.
    Use a Sprinco orange spring with the Kaw Valley buffer for a .308. Buffer tube has to be the std AR15 tube length (7" inside depth) for this setup. This assumes the buffer is 2.5" long.
     

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    BLEE

    NOBODY
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    Jan 29, 2020
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    Get a pencil profile 16" barrel, in .308, if you're thinking about hunting. Large frame ARs are pigs and generally need to be fired from bipod. I think my Aero M5, 6.5CM, 22", easily weighs 15lbs, with scope and bipod.
     
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    Forrest

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  • Feb 16, 2018
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    Fresno
    Save yourself some grief. Make sure the buffer and buffer spring are correct (DPMS Rifle). Use only an adjustable gas block. Preferably a clamp on adjustable gas block. Pay attention to MTRMN's picture above. There is no standard for .308/6.5cm gas port locations for barrel manufactures. They use both AR gas length gas ports and Armalite gas port lengths. These two use different length gas tubes. Using the wrong gas tube will result in malfunctions that will drive you nuts. Criterion barrels are my first choice. Make sure and use a Aero Precision Extended Magazine Release/Catch Button and Aero Precision M5 .308 Bolt Catch. A typical AR 15 lower parts kit will come with a magazine catch that is short about 4 threads for use on a AR10. AR10's are fat unlike AR15's. That's why you need the AP extended mag button. It has the extra 4 threads you need to adjust it to work. Standard AR 15 bolt catches usually won't tip up far enough to catch the AR 10 BCG when the magazine is empty resulting in the BCG going forward on a empty chamber. The AP M5 Bolt Catch will tip up far enough to lock the BCG back on a empty magazine. VG6 muzzle brake's work great.

    .
     
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    Bocephus1776

    Private
    Minuteman
    Nov 14, 2020
    13
    1
    Missouri
    Save yourself some grief. Make sure the buffer and buffer spring are correct (DPMS Rifle). Use only an adjustable gas block. Preferably a clamp on adjustable gas block. Pay attention to MTRMN's picture above. There is no standard for .308/6.5cm gas port locations for barrel manufactures. They use both AR gas length gas ports and Armalite gas port lengths. These two use different length gas tubes. Using the wrong gas tube will result in malfunctions that will drive you nuts. Criterion barrels are my first choice. Make sure and use a Aero Precision Extended Magazine Release/Catch Button and Aero Precision M5 .308 Bolt Catch. A typical AR 15 lower parts kit will come with a magazine catch that is short about 4 threads for use on a AR10. AR10's are fat unlike AR15's. That's why you need the AP extended mag button. It has the extra 4 threads you need to adjust it to work. Standard AR 15 bolt catches usually won't tip up far enough to catch the AR 10 BCG when the magazine is empty resulting in the BCG going forward on a empty chamber. The AP M5 Bolt Catch will tip up far enough to lock the BCG back on a empty magazine. VG6 muzzle brake's work great.

    .
    Why the clamp on style gas block? I'm not questioning you, I'm just a naturally inquisitive person and enjoy knowing the why on things. Thanks for the info.
     

    Kickin45

    Deaf dumb and blind
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  • Oct 7, 2018
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    Buy a Gen 2 lower from PSA. Then buy a Gen 2 upper from PSA.
    Then “assemble” them together. All problems solved 👍

    And I do mean “problems”. I’ve got a LR308 that I built from the ground up. Spent over a year now working out the bugs and it still isn’t right. It has a total of 4 rounds down the pipe. Take lessons from others experience.
     

    vinniedelpino

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  • Sep 27, 2020
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    Charlotte NC
    Hi y'all. I'm building my dad a LR-308 and was wanting some advice. I've built about 10 AR-15's and a couple AR-9's but I know the large frame is a whole other beast. It's mostly going to be for fun and maybe some white tail hunting. Most shots 50-100 yards. We have a spot where we can reach 200 but it won't be something very often ( the property is a couple hours away). I'd like to build with the ability to reach 500 in case one of us gets some property. Here's what I've got

    I have:
    Lower = American Made Tactical
    Upper = American Made Tactical DPMS low pro
    BCG = Fail Zero Nickel Boron

    Parts I'm looking at:
    LPK = CMMG MK3 kit
    Trigger = Rose Armament RA-434
    Buffer group = KVP carbine tube with 5.6 oz buffer
    Stock = MFT Battlelink (he has it on his 5.56 and wants it the same)
    Gas Block = probably Faxon or Aero unless y'all recommend an adjustable

    And now for the big question;
    For the barrel I was looking at the Faxon 20" heavy fluted (p/n: 10B810R20FHQ-5R-NP3) or the Wilson Combat 20" Super Sniper fluted (p/n: TR-308SSRG20FT10) . Everywhere has been out of stock for at least 8 months. Should I wait until one of these comes available or is there another option for around $350?

    Also, I'm going to build one for myself as well with pretty much all the same parts except I think I'm going with the PRS stock and I'm willing to spend between $500-600 for the barrel if the extra money is worth it. I was looking at the X-Caliber barrels but they seem to have mixed reviews on here.

    My experience with Xcaliber has been good, but that's limited to a savage small shank prefit spun by crown ridge. I've heard bad things as well.

    IMO, you can't go wrong with criterion and they can be pretty easily had for around $300. I just bought a 22" 6.5 creed for a LR-308 build for $301 from creedmoor sports and I don't think there's anything that will outperform unless you pay twice as much. With a bolt gun I think it's easier to pick up the differences with a phenomenal barrel and a "good" barrel. There's a lot that goes into the accuracy of a gas gun. I also have a 20" wilson combat in 1/8 that shoots .6-.7 moa with 69gr in .223. No complaints there either. I'd skip the faxon altogether...

    I'd also try to find a barrel matched to the bolt, stick with the adjustable, clamp on gas block as mentioned, and maybe even grab some .001" shim stock for the barrel extension to receiver fit. I don't true the receiver face. I wouldn't say they're hard to build if you know what parts are compatible, it's just that they're harder to tune to get running optimally. You can get away with cheap parts on an AR-15, not so much with an AR-10. In my experience, anyway.

    Expect some "oh shit" moments along the way, but you'll get it where you want it to be.
     

    BLEE

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    Jan 29, 2020
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    I didn't build mine. I bought an Aero lower, on sale, then bought the complete upper, less bcg, on sale. I added an Aero BCG, Magpul PRS, MBT2S, Seekins mount and a Riton Mod7 (Woot special). I used a Sprinco Orange spring and a carbine tube. Other than my DA error of reversing a FCG spring, it runs like a clock with Hornady American Gunner, ejects @ 4 o'clock, six feet away, every single time. I kept the Aero fixed gas block. It seems to be tuned, just about perfectly for the rest of the rifle. Now, if only I could shoot worth a crap.... that's another story. Lol
     

    Forrest

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  • Feb 16, 2018
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    Fresno
    Why the clamp on style gas block? I'm not questioning you, I'm just a naturally inquisitive person and enjoy knowing the why on things. Thanks for the info.
    Set screws could come loose and pined on gas blocks are very hard to work on if you have to remove them. A clamped on gas block is tight all the way arounds and the set screws on a set screw gas block are forcing one side of the gas block away from the barrel. In order to install a set screw gas block the gas block inner diameter has to be very slightly larger than the barrel to slide it on the barrel. This is not a perfect fit. I guess I'm a little anal.
     
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