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Building rifle length AR 15 vs Carbine AR 15

Discussion in 'Gunsmithing and Repairs' started by RussellC, Mar 17, 2017.

  1. RussellC

    RussellC Member

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    All the AR 15 rifles I have built have been carbine length, both .223 and .300 Black Out.
    They used the typical 6 position Mil spec tube and Magpul CTR stock, carbine spring and buffer.

    I have just bought an 18" SPR barrel that is rifle length. Other than the rifle length gas tube, what differences are there as to spring and buffer weight, and if so what should I be looking for? I would like to retain the 6 position type stock if possible, if not no big deal, what should I use? I see a lot of SPR or DMR builds using fixed stocks...

    Thanks in advance,

    Russellc
     
  2. entropy

    entropy Member

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    Standard mil-spec buffer and spring for which ever of the two stocks I recommend, should be fine, and your choice of A1 or A2 stock is my recommendation.
     
  3. RussellC

    RussellC Member

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    So to be clear, are you saying that the 6 position stock, spring and buffer will work, just that you recommend the fixed A1 or A2?

    Russellc
     
  4. Blue68f100

    Blue68f100 Member

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    Yes, the same 6 position stock will work just fine, just use the right buffer for which stock you run.

    You will get better accuracy with a fixed stock, my experience. That is the only difference except with the rifle gas system you will have slightly more velocity. I run adj gas blocks on my guns. There fine tuned to each gun for the loads I shoot.
     
  5. LoonWulf

    LoonWulf Member

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    a1 and a2 stocks require a rifle length buffer tube, buffer, and spring dont they? ive never used a fixed stock on an AR.
    Ive got an ATI Taclite stock on my personal lower (im weird i know, only one ar lower, and no .223 upper), Ive shimmed it so wiggle is minimal and ive had good results with both my .458 and 6.5G. I havent tried it but im pretty sure you could shim most of the adjustable stocks to achieve less movement, but if compact isnt necessary (and adjusting length), than a fixed stock is most likely the way to go for a precision rifle build.
     
  6. RussellC

    RussellC Member

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  7. entropy

    entropy Member

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    Correct.
     
  8. RussellC

    RussellC Member

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    The Barrel (rifle length Ballistic Advantage 18" SPR, 1/7 twist) is to be delivered tomorrow, I am putting it on an Anderson upper. I will try it with my standard carbine lowers, Spikes tactical (2) or a Seekins Lower all of which use Spikes adjusable stock, buffer tube, spring and buffer, Mil spec carbine, w/ Magpul CTR stock and see how it works.

    If it has cycle problems, I'll be back....think I will use an adjustable gas block? Also will install the SSA trigger once function is sorted.

    Russellc
     
  9. BBBBill

    BBBBill Member

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    Looks like you're intent is to mimic the enhanced accuracy of the military SPR. If so pay particular attention to the fit of the barrel in the upper. Many barrel extensions are not as tight (diameter) as they should be in the upper. Just torqueing the barrel in does not eliminate that point of potential movement. Depending on the amount of difference in the upper ID and barrel extension OD, pro builders will use anything from Loctite to shim stock to fill the gap. Truing the face of the upper might be in order, too.
     
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  10. RussellC

    RussellC Member

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    I am assuming that "truing the face of the upper" sounds like something for a gunsmith, or no? This, and the shimming the barrel mentioned interest me, I have never heard of this. I guess I better search around and finds a place to learn more on accurizing the AR.

    I have only put on 3 barrels, one was on a Cerakoted upper, it was tight enough to need tapped in.
    The other 2 were not that tight, but quite snug. What sort of tolerances are we talking about that need shimming?

    Thanks,

    Russellc
     
  11. Cemetery21

    Cemetery21 Member

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    http://www.brownells.com/gunsmith-t...16-upper-receiver-lapping-tool-prod20220.aspx
    If you have already done 3 uppers, this might be worth the investment. I true every upper now. Some need only a touch and others take more. Read the instructions and keep the cutting compound out of the receiver bore.
    Snug is fine for me for the extension fit. I have used blue Loctite on some that were loose fit. Keep the Loctite away from the barrel nut threads.
     
    Last edited: Mar 19, 2017
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  12. BBBBill

    BBBBill Member

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    The March and April 2013 issues of American Gunsmith cover this specific subject. Over about a one year period Joe Carlos, former chief gunsmith of the USAR team and a former world record holder, wrote a series of articles published in the American Gunsmith magazine on match tuning the AR. Basically you want zero play between the barrel extension and upper. Preferred method is an extension that is machined to a match fit to your receiver. Hand selected is next best, then shims and/or Loctite. If it's only half a thou to a couple thou then Loctite. If the clearance is enough to need shims then three spaced evenly around the extension with Loctite to hold everything together. Some will say that this is only for match guns, but it in no way affects reliability. Does make it a pain to pull the barrel.
    I've built up one gun using this technique. Not much of a sample, but it did reduce groups from 3-1/2" to 1-1/2" with the Colt factory barrel. No other accuracy work was done to the barrel and upper. The lower has a Rock River trigger and one of those round red things that you stick in the lower behind the safety to take the wobble out of the upper/lower.
     
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  13. RussellC

    RussellC Member

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    I purchased from Brownell's the lapping compound and the lapping tool. D-Tech's stuff is the bomb, and I would eventually like to have one of his uppers, but they are a bit expensive, (although
    not that bad really) right now.

    Is only the receiver lapped, nothing to the barrel end?

    Russellc
     
  14. RussellC

    RussellC Member

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    What is the recommended material for the shims? I've got the blue lock tite. How difficult is this to undo? I have never taken one apart, just wondered.

    Thanks in advance,

    Russellc
     
  15. RussellC

    RussellC Member

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    Barrel is a very snug fit, it will have to be tapped in, so has not been fully seated yet.

    Russellc
     
  16. BBBBill

    BBBBill Member

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    You can buy shim stock from a local machinery supply or online. Or just pick up a cheap set of feeler gauges to cut up for shims. With blue Loctite should be nothing more than removing the barrel nut from the receiver and a couple quick raps on the receiver with a non-marring plastic hammer while the barrel is clamped in a barrel vise (or on the barrel if the upper is held in a clamshell receiver vise). With a different grade of Loctite it might require some heat from a heat gun. Just enough to make the Loctite smoke, indicating that it has given up its grip. That much will not harm the gun.
     
  17. Everready73

    Everready73 Member

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    You may want to run a heavier "H" buffer instead of a carbine buffer. If you have any try both and see what works best with the gas system. If you want to try something different and make it a little "softer" shooting look into the Vltor A5 buffer system. It is longer than a standard buffer tube and uses there special buffer and spring. Very good feedback on these
     
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  18. Cemetery21

    Cemetery21 Member

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    Is only the receiver lapped, nothing to the barrel end?

    Russellc[/QUOTE]

    Yes, the Brownells' tool (and others made similarly) only lap the receiver. I think it would take a machinist/gunsmith to check/square the barrel extension to the bore. That's something I've not done. If you went that far, I think you would also want to have the bolt, chamber, receiver threads and barrel nut checked/squared.
    I've had similar work done on bolt actions, but not ARs.
     
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  19. Malamute

    Malamute Member

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    In discussions elsewhere, its been often mentioned that BCM uppers tend to be snug on barrel extensions.

    As for carbine stocks and receiver extensions, Ive always found the rifle stocks feel more solid to shoot. Even the Magpul CTR stock doesn't remove all the wobble. A standard carbine stock feels like a wobbly underfolder AK stock to me compared to a rifle stock. In shooting at distance, there was a noticeable difference in how well, or even if I could, spot my hits through the scope at 600 yards with a 2-7x scope. With a rifle barrel (20" govt profile Colt A2) and rifle stock, seeing the hits seemed like shooting a 22 with how steady it felt. With a mid gas 16" medium heavy barrel and S&W carbine stock, I wasn't able to see the hits nearly as well, sometimes not at all. The difference in muzzle blast is very noticeable to me also, but I already have pretty bad hearing loss, and may be more bothered by blast. If I have a choice, and compact isn't the overriding concern, I prefer rifle barrels and stocks. To me, they are far more fun and interesting to shoot.
     
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  20. RussellC

    RussellC Member

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    The Ballistic Advantage barrel is a very snug fit, the extension is coated with Nickel-boron and while I understand it is a very thin treatment, I
    suspect this is why it is so snug. It will definitely need tapped in. I dont think it will come out (easily) if I put it in, so I am not going to until the lapping is done to the receiver face. I need to get the clam-shell type upper clamp, mine insets and uses two pins and works great for some things, but this lapping device seems to rely on a bolt carrier to square it, and you cant get a bolt into the receiver with my type...no biggie, I will get that style.

    Russellc
     
  21. Malamute

    Malamute Member

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    Sounds like youre on the right track.
     

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