Does Aero Precision AR308s do anything different than the others?

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Minuteman
    • Oct 11, 2013
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    #1
    Decided on a collapsible (carbine) stock for this new Aero 6.5 gas gun build and the bolt won't go all the way back to lock open; it's about a quarter inch short. The buffer springs bottoming out and I can not figure out why. I know the whole "there's no single spec for ar308s/ar10s" thing, but finding out what's compatible and what's not seems to be pretty challenging. I keep seeing that the buffer tubes and buffer springs are compatible, but buffers are not. So, then how does this carrier tail bottom out? The tube's Strike Industries, the buffer's an adjustable Expo Arms, and the springs a no name AR15.
    So during my research, the only thing I found was that on Aero's website, their 308 carbine spring has a different part number than their AR15 carbine spring... but when shopping on all the ar parts websites, they all list (except for aero) all the same springs for the 308s and 556s...
    Called Brownells and they list the OAL's for the springs in their notes, and the 308 springs thicker and longer lol. Would Im imagining would exacerbate my issue (if those measurements are correct) or does the 308 spring have so fewer coils that it maintains a shorter compressed OAL...

    Has anyone built one from the ground up on an Aero set and run into this same problem?
     
    #8
    loclass said:
    Are you using a standard ar15 buffer in a standard 7" buffer tube? If so you have the wrong buffer. If you're using a 7" carbine buffer tube on an LR308 then you need the "shorty" lr308 length buffer.
    Click to expand...
    Typically Aero 308 uses a AR15 carbine buffer tube... and that requires a 2.5" buffer be used.

    IE, the longer "308" BCG needs extra room to fully compress into it.

    Just adding specific OAL buffer length.
     
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    #10
    Here's some fodder for you to read, scroll down and there is a list of measurements for tubes, springs and buffers. I just know that when I built my first large frame AR, I heard the term, "There is ¢.75 difference between Large Frame AR buffer tubes", turns out if you wind up with the longer one, 3 quarters will fix the problem.

    Compatibility Large Frame ARs
     
    Last edited:
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    #11
    Basic user said:
    I'm using the user adjustable Odin Works 308 buffer. That's correct right?
    Click to expand...
    Carbine RE on a large frame, requires a "308 carbine" spring and a 2.5" length buffer.

    You did not get any of those things by removing them from any ar15. Maybe the tube.

    The longer (3.5"?) buffer found in ar15 type rifles, will work in large frame when using an A5 RE.

    The last option is a rifle length RE, 308 rifle spring and buffer.

    Once you have that part figured out, then you can tackle the rest.

    When i built my ar10, I used the rifle system and a prs3. I switched out the Carbine system after trying to fire some 2700fps bolt gun loads that were popping primers out in the ar10. AGB helps a lot, but is not necessary
     
    #12
    AMGtuned said:
    Carbine RE on a large frame, requires a "308 carbine" spring and a 2.5" length buffer.

    You did not get any of those things by removing them from any ar15. Maybe the tube.

    The longer (3.5"?) buffer found in ar15 type rifles, will work in large frame when using an A5 RE.

    The last option is a rifle length RE, 308 rifle spring and buffer.

    Once you have that part figured out, then you can tackle the rest.

    When i built my ar10, I used the rifle system and a prs3. I switched out the Carbine system after trying to fire some 2700fps bolt gun loads that were popping primers out in the ar10. AGB helps a lot, but is not necessary
    Click to expand...
    That site is saying there different sizes of buffer tubes for the AR10 and 15; are they grouping the AR308 in with that?
     
    #14
    hlee said:
    The ar15 carbine buffer is longer than the lr308 buffer. You need a different/shorter buffer.
    Click to expand...

    He's already too short, remove the spring and follow these instructions to eliminate the spring as the culprit

    IMG_5223.jpeg




    Buffer/Tube issues
     
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    #15
    Basic user said:
    That site is saying there different sizes of buffer tubes for the AR10 and 15; are they grouping the AR308 in with that?
    Click to expand...
    Diameter; no, not that I'm aware of.

    Length; I'm also quite certain that Carbine is carbine, a5 is a5, and rifle is rifle.

    Spring and buffer are different.

    Aero Precision themselves sell the carbine "kit" you need. Matter of fact, there's one on my rifle now because I didn't have another rifle system for it. It's a carbine RE, 2.5" h3 buffer, and 308 carbine spring.
     
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    #16
    Wrong spring.
    An M4/AR-15 carbine spring will not work with a 308 short carbine buffer (2.5" OAL) in a M4/AR-15 carbine receiver extension (7" inside depth).

    The maximum allowable compressed spring length of a 308 short carbine buffer is around 2.000"-2.125".
    An M4/AR-15 carbine spring with 37 coils and a wire diameter of 0.072" is 2.736" long at full compression.
    An AR308 carbine spring with 26 coils and a wire diameter of 0.075" is 1.950" long at full compression.

    Dimensions listed can vary between manufacturers and allowable variances/tolerances.
     
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    #20
    Shooter McGavin said:
    www.aeroprecisionusa.com

    M5 .308 Carbine Buffer Kit

    Shop M5 .308 Carbine Buffer Kit, No Stock and more online at aeroprecisionusa.com. Free shipping on all orders over $99.
    www.aeroprecisionusa.com www.aeroprecisionusa.com
    Click to expand...
    If he uses that kit he needs to throw that light buffer away and buy this:

    He will be mighty unhappy if he picks up a 22” rifle gas 6.5CM upper that Aero sells and will be really disappointed if he pairs it with the Aero buffer kit quoted above while keeping the 3oz buffer.
     
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    #21
    TBH, if you are using an Aero upper and lower, just purchase the Aero buffer system (tube, buffer and spring) and an Aero BCG and you should be G2G.

    FWIW, the Aero .308/6.5CM nitrided bolt claims to be a "HP" bolt, i.e., smaller diameter firing pin and firing pin hole. It is smaller than the typical .308 bolts, but not as small as the JP's....
     
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    #24
    Ok, now that I had the time to fuck with this thing, the buffer's 9/16" too short; the carrier body's slamming into the lower receiver/buffer tube threads. I just dont understand lol. I can see plus or minus a quarter's worth of length, but 9/16ths inch?
     
    #25
    FWIW, others gave you valid suggested resolutions to the problems you have encountered. The easiest fix is to just use Aero buffer system parts in your Aero receiver. For this latest issue you report, it was previously suggested to use some inserted quarters in the buffer tube before inserting the buffer spring so they act as "spacers". The actual amount to use is determined by trial and error until resolved. If you are already seeing indications that the BCG has/is impacting the receiver body that the buffer tube threads into, you need to check for cracks that may have resulted. It could lead to a catastrophic failure under use.
     
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    #27
    They are not that difficult.

    You need to pay attention to what you are doing and source your parts wisely. If you don't want to take the time to research the parts you are using, single source them to ensure compatibility and functionality.

    You can't just buy a bunch of crap, from different sources, toss it together and expect it to work.
     
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    Reactions: Basic user, GhostFace and r.tenorio671
    #29
    r.tenorio671 said:
    FWIW, others gave you valid suggested resolutions to the problems you have encountered. The easiest fix is to just use Aero buffer system parts in your Aero receiver. For this latest issue you report, it was previously suggested to use some inserted quarters in the buffer tube before inserting the buffer spring so they act as "spacers". The actual amount to use is determined by trial and error until resolved. If you are already seeing indications that the BCG has/is impacting the receiver body that the buffer tube threads into, you need to check for cracks that may have resulted. It could lead to a catastrophic failure under use.
    Click to expand...
    I do know about throwing a few quarters in to alleviate that problem, but it's more than a few quarters off; I wouldnt feel comfortable putting like 10 quarters in there to take up that space. From what I gathered I had all the correct parts, and it was just the spring that was the last part that needed correction. And I haven't fired this yet, I was just pulling the charging handle back to check function when I noticed it hit the lower and the buffer tube. It's not bad but you can see where the anno was compromised. No biggie though.
     
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