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Thread: 16" 308 AR: larue obr or a ga precision gap 10?

  1. #1
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    16" 308 AR: larue obr or a ga precision gap 10?

    16" 308 AR: larue obr or a ga precision gap 10?

    here are some things i'm tossing around in my head.

    the obr is lighter from the internet sources for weight. I have handled one with a prs and us optics glass. it was handy enough. I didn't find it heavy.

    gap 10 has ambi bolt release. obr could have the ambicatch installed. both could use a raptor charging handle.

    the gap 10 is heavier. is it worth it even though it is heavier?

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    I've put a few hundred rounds through 16" OBR's but I personally bought the LaRue 18" predatOBR (and an LMT MWS). I'm not a fan of the new trigger LaRue is using but it shoots great and handles very nicely. Sorry I can't comment on the GAP.

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    What are you looking to do with it?

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    Quote Originally Posted by anubismp View Post
    What are you looking to do with it?
    I forgot to say in the initial post.

    would like it to be a maximum precision rifle (sub moa using factory loaded ammunition) while running 3-15x glass, but at a limited range: 0-600 yards. no plans for extended range shooting.

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    When looking for precision heavier in my experience is better as it keeps you more steady. With that being said I don't feel you can go wrong with either.

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    You're cutting the nuts off a .308 to go 16". It becomes less of a precision rifle when you slow it down. Trajectory-wise, you may as well be shooting an 18" 5.56 out to 600. Honestly, my 18" OBR suppressed is barely up to speed. I somewhat wish I'd have gone 20" at this point.

    The GA Precision is probably going to be a more accurate rifle and it is customizable at the shop---but I have heard that they can be finicky with ammunition selection. You'll probably get it faster. LaRue seems to be more aimed toward a durable, robust rifle.

  7. #7
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    I have a 16" OBR with Surefire brake, SOPMOD stock, and Schmidt&Bender 4-16x PM-II in a Spuhr 4002 mount (0moa cant, 1.46" height). It only has about 500 rounds through it, a mix of Black Hills 175gr OTM, Fed GMM 168gr OTM, and surplus Portugese 147gr fmj. It has been totally reliable and very accurate. The factory test target was .590" at 100yd. I have been able to essentially duplicate that at 100 with BH. I shot with a friend last weekend out to 554 yards and was rather boringly ringing steel at 400 and 554 yards with both 175gr BH and even with 147gr Port.

    My only gripe with the obr is the additional rail height, which necessitates a lower optic mount if you want to avoid using a PRS or the LaRue RISR.

    I would most certainly go with a 16" barrel. You really give up very little between a 16" and 20" barrel when it comes to velocity. Just ask the guys at KAC their thoughts on this. Both KevinB and Failure2stop have said on several occasions that they see no reason to go with anything longer than 16" in a 7.62x51mm gas gun. My OBR chrono'd a 5 shot average velocity of 2374 for 175gr BH, my buddy's load (m118lr equiv) chrono'd 2421 in his rifle.

    As far as optics go, my friend has a Leupy mk6 3-18x with H58 reticle. This is a great scope and it is rather reasonably priced considering the glass quality, the nicely designed turrets, and that it is made in the US. It is also very light at 23oz without a mount. If I were in the market for an optic right now, the mk6 3-18 would be it. I would opt for the lower profile turrets.

    The GAP I cannot help you with, other than to say I absolutely despise the rail system they use. Other than that, they consistently get high praises.

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    My 18" does 2540fps with that ammo unsuppressed and 2570 suppressed. I really don't see 10% velocity loss as very little. At longer ranges this really makes a significant difference. Especially in the wind. At 1k and 90 degrees 10mph, this is .4 mil more of wind drift . .4 MIL----that means you miscalled the wind by 2 MPH you completely miss, but it would have been a hit with a 20".

    Seems like you give up a lot to me. Maybe at 500 yards it makes no difference but at that range what is the point of a .308? Even if you're only shooting to 600, the velocity is nice to have to help defeat the wind. Who knows, you may get the opportunity too ago farther later. You did say you wanted MAXIMUM precision.

    Ask yourself, do you intend to make first round hits in all conditions or is it a range toy that 2-4" extra is going to make it so much easier to carry from your trunk to the bench at the range?


    Certainly agree, MK6 3-18x is pretty awesome scope for the money. The weight is awfully handy.

    My rifle wears a S&B 5-25x. If I wasn't used to it from running them on my competition gun, I'd pick up a MK 6 and some lower rings and ditch the PRS stock.


    Sent from my iPhone using Tapatalk

  9. #9
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    Quote Originally Posted by tylerw02 View Post
    You're cutting the nuts off a .308 to go 16". It becomes less of a precision rifle when you slow it down. Trajectory-wise, you may as well be shooting an 18" 5.56 out to 600. Honestly, my 18" OBR suppressed is barely up to speed. I somewhat wish I'd have gone 20" at this point.
    There is very little velocity difference between 16" and 12" 7.62.
    With M118LR, '05 lot, I see ~2500 out of the 16" and ~2600 out of the 20", with no loss of pure precision by dropping barrel length.
    I have test results for literally thousands of guns, and I see no reason to go longer than 16" for a 7.62. Of course, that doesn't mean that anyone is wrong for wanting to get that extra 100fps, just that for me, for use out to 1,000 meters, there is no practical advantage to 100 fps, where there definitely is an advantage to a shorter, lighter gun.

    Input Data
    Manufacturer: Sierra
    Description: HPBT MatchKing™
    Caliber: 0.308 in
    Weight: 175.0 gr
    Ballistic Coefficients: 0.485 [0-1800], 0.496 [1800-2800], 0.505 [2800-5000] G1 (ASM)
    Sight Height: 2.70 in
    10mph 90 Degree Wind

    2500fps:
    Range___Drop____Drop____Windage___Windage
    (m)_____(in)_____(mil)______(in)_______(mil)
    0_______-2.7____***______0.0________***
    100_____-0.0____-0.0______0.9________0.2
    200_____-5.1____-0.6______3.9________0.5
    300____-19.3____-1.6______9.1________0.8
    400____-44.4____-2.8_____16.9________1.1
    500____-82.5____-4.2_____27.5________1.4
    600___-136.2____-5.8_____41.5________1.8
    700___-208.6____-7.6_____59.1________2.1
    800___-303.5____-9.6_____80.4________2.6
    900___-425.3___-12.0____105.6________3.0
    1000__-578.3___-14.7____134.4________3.4

    2600fps:
    Range___Drop____Drop____Windage___Windage
    (m)______(in)____(mil)______(in)______(mil)
    0_______-2.7____***_______0.0______***
    100_____-0.0____-0.0_______0.9______0.2
    200_____-4.5____-0.6_______3.7______0.5
    300____-17.4____-1.5_______8.6______0.7
    400____-40.2____-2.6______15.9______1.0
    500____-74.9____-3.8______25.9______1.3
    600___-123.8____-5.2______39.1______1.7
    700___-189.8____-6.9______55.7______2.0
    800___-276.3____-8.8______75.9______2.4
    900___-387.4___-10.9_____100.1______2.8
    1000__-527.4___-13.4_____128.0______3.3

    So, what we really see is an additional 1.3 mils of drop at 1k, and only 0.1 mils of increased wind drift at 1k.
    While the 1.3 mils/21 inches of increased drop at 1k looks to be significant, a shooter will need fairly accurate range estimation to successfully hit targets past 400 meters even with a 20" 7.62.
    The 16" barrel will have about 17" of drop between 990 and 1000, while the 20" will have 15.4". Effectively, 4" of barrel only gets you 1.6" of performance difference at the limits of the cartridge.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  10. #10
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    My math, according to Ballistic AE in my current AO says the 16" is giving up .4 mRad of drift at 1,000 yards (12.5") using the fellow who owns a 16" OBR's numbers of 2374 fps with Black Hills 175 gr.

    My real world 18" gun runs Black Hills 2570 suppressed, using backward math on Ballistic AE.

    In the context of getting real world 2500 out of box ammo, in a 16", I'd say you're right(---but that doesn't seem to be happening), the difference is .2 mRad of wind drift today, in my AO----or 5.3". But the reality is with box ammo, 16" OBRs aren't getting 2500 fps. They are getting upper 2300s and low 2400s, which is pretty damn slow. I supposed the KAC guns are faster and that's a different ballgame---I can't speak as to that, you're much, much more qualified to say so. We both know wind is our biggest issue, not range calculation.

    Just like the velocities aren't game-challengingly different, neither are the couple ounces saved of a 16" vs 18" vs 20". But shooting a 12" gong, a miscalc of 2 mph wind with a 16", a 20" makes a hit. On the KAC rifle, what is the difference in weight between a 16" barrel and a 20"?


    To the OP, the 20" will give you more options and more flexibility; the ability to shoot further in more wind because you're not going to be using a ton of M118LR I'd assume. It will also prove much more useful should you choose to switch to handloaded ammunition. It seems to me, if you want MAXIMUM accuracy, you should contact George Gardner and order a GAP 10 and take his advice on barrel length.
    Last edited by tylerw02; 02-13-14 at 18:02. Reason: No reason to quote, post calculations from a different calc....redundant

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