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  1. #1
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    308 Aero M5 build questions

    Looking at rails for building up my Aero M5 Freedom set. At SLR they list DPMS high and DPMS low. What is the difference? And is there anything proprietary about the M5 set I need to know about? I bought the MI lower parts kit.

    How about an alternative to the $200 Geisele 308 reaction rod? This Creedmoor will likely be my only large frame build.

    https://www.slrrifleworks.com/
    “What in the world is a moderate interpretation of a constitutional text? Halfway between what it says and what we'd like it to say?" -Antonin Scalia

  2. #2
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    You want the DPMS Hight for the M5 set. The difference is literally the height of the top rail. With the "low", the top rail will step-down a tiny bit from the receiver.

    I would have strongly suggested using the Aero M5 LPK. At a minimum, you'll want to use the Aero M5 pivot pin which is a touch longer than a standard DPMS pattern pivot pin. Some LPKs may give you issues with the bolt catch and mag catch. If so, get the Aero parts (the mag catch is extended).

    Just use a barrel vise block to mount the barrel and you'll be fine.

    Edit: I know a few will disagree with me here, but for a large frame build I recommend just starting off with an adjustable gas block, too (I recommend SLR Sentry).

    And while I'm at it, here is a killer deal on a BGC: https://www.armorally.com/shop/toolc...black-nitride/

    The easiest thing to get wrong on Large Frame builds is the receiver extension and buffer. Aero's M5 carbine kit uses a AR15 buffer tube w/ a DPMS style 308 buffer (shorter than the standard AR15 buffer) and works fine. Alternative, Aero sells an M5 "rifle" extension buffer tube/buffer. You can also use an Armalite length buffer tube but that uses a standard AR-15 buffer. Be careful you don't mix/match or you can do some damage to your lower or it just won't cycle.
    Last edited by BoilerUp; 30 August 2018 at 06:31.

  3. #3
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    I always order the extended Magazine button, Aero's M5 take down and pivot pins, and throw the bolt catch on my order for M5's.

  4. #4
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    Quote Originally Posted by Uffdaphil View Post
    Looking at rails for building up my Aero M5 Freedom set. At SLR they list DPMS high and DPMS low. What is the difference? And is there anything proprietary about the M5 set I need to know about? I bought the MI lower parts kit.

    How about an alternative to the $200 Geisele 308 reaction rod? This Creedmoor will likely be my only large frame build.

    https://www.slrrifleworks.com/
    I went through this with MI on the rail height. First, just just call the vendor, they probably know. With MI, I just took a depth gauge and measured off the upper rail TDC of the barrel receiver (not sure what you call it, technical, but the part of the receiver the barre fits in). Called them, cave them the spec and they sent me the right one. As already mentioned, it's just approx. .075 or so difference in the two. Of course we're talking different vendors, so I can't speak about SLR, but I can bet you they've been asked the same question more than once, give 'em a call or shoot them an email and they can probably pick the right on for your Aero set with just a phone call.

    FT
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  5. #5
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  6. #6
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    That was quick. Thanks guys. Good ideas.

    I had MI on the brain when I typed. Fortunately I did get the M5 LPK not the MI. This build is a ways off as my safe is crammed full and the Visa needs time to heal. Just got the barrel today for my Centurion group-buy components so that is ahead in the queue.
    “What in the world is a moderate interpretation of a constitutional text? Halfway between what it says and what we'd like it to say?" -Antonin Scalia

  7. #7
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    I got a Centurion 14" CMR and went with the Vltor RE route.
    "And now you understand. Anything goes wrong, anything at all... your fault, my fault, nobody's fault... it won't matter - I'm gonna blow your head off. No matter what else happens, no matter who gets killed I'm gonna blow your head off." -Big Jake

    "All the Gods, all the heavens, all the hells, are within you." -Joseph Campbell

    Instagram- @tomcheaney9

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    Tom, I love CMRs (have three), but the I.D. is likely too small for an adj gas block. The SLR has an extra .25”.

    Is this the Vltor RE you are using? What spring? Standard sized A5 buffer?
    https://www.vltor.com/shop/featured/...ver-extension/

    EDIT: I have a Sprinco orange extra power DPMS spring, but it requires the std 7” carbine tube and short buffer. Opinions on which setup would have better felt recoil? Remember this will be for an 18-20” Creedmoor.
    Last edited by Uffdaphil; 3 September 2018 at 12:30.
    “What in the world is a moderate interpretation of a constitutional text? Halfway between what it says and what we'd like it to say?" -Antonin Scalia

  9. #9
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    The VLTOR A5 buffer tube is simply an Armalite AR-10 carbine sized receiver extension with a specially designed buffer for the AR-15. If you use an Armalite carbine receiver extension (i.e., an A5), on a large frame build, you need to use a standard AR-15 carbine buffer and the Armalite buffer spring (https://www.rainierarms.com/armalite...buffer-spring/). If you use the A5 buffer, you likely won't cycle properly, and if you use the DPMS 308 carbine buffer (the short one), the bolt will slam into the lower receiver and cause damage. If you ever seen damage to the threads on the lower where the buffer tube threads in, you've got a mismatched buffer setup. Guess how I know that.

    I'm slowly equipping all my ARs with JP silent captured springs for "better felt recoil". Those things are nice. Haven't shot a large frame with one, yet, though.

    I run an SLR Sentry 7 under a SLR 15" Ion lightweight. No problems with clearance.

  10. #10
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    Quote Originally Posted by Uffdaphil View Post
    Tom, I love CMRs (have three), but the I.D. is likely too small for an adj gas block. The SLR has an extra .25”.

    Is this the Vltor RE you are using? What spring? Standard sized A5 buffer?
    https://www.vltor.com/shop/featured/...ver-extension/

    EDIT: I have a Sprinco orange extra power DPMS spring, but it requires the std 7” carbine tube and short buffer. Opinions on which setup would have better felt recoil? Remember this will be for an 18-20” Creedmoor.
    You have any 308 CMR's? I bet you could sneak an adjustable under there. Not quite the slim profile of an AR15 version.

  11. #11
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    The .308 CMR I.D. is 1.25” and Sentry 7 is 1.40” so no go. As for the RE, I’m going to get more input on the Creed forum before I commit. I’ll post pics when finished. Probably after next quarter’s dividend at least.

    Thanks all for the clarifying info.
    “What in the world is a moderate interpretation of a constitutional text? Halfway between what it says and what we'd like it to say?" -Antonin Scalia

  12. #12
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    Quote Originally Posted by Uffdaphil View Post
    The .308 CMR I.D. is 1.25” and Sentry 7 is 1.40” so no go. As for the RE, I’m going to get more input on the Creed forum before I commit. I’ll post pics when finished. Probably after next quarter’s dividend at least.

    Thanks all for the clarifying info.
    Hey sorry about late responses, been busy at work and catching stuff up around house.

    That is the correct RE Im using with Armalite's AR10 Spring (they use it for Rifle and Carbine AR10s) and a H Buffer.

    I run an adjustable GB under my CMR, but its not a Sentry. Its a Odin Works its a close fit but doesn't touch. I think I have pics somewhere. If not then I'll post some for ya.
    "And now you understand. Anything goes wrong, anything at all... your fault, my fault, nobody's fault... it won't matter - I'm gonna blow your head off. No matter what else happens, no matter who gets killed I'm gonna blow your head off." -Big Jake

    "All the Gods, all the heavens, all the hells, are within you." -Joseph Campbell

    Instagram- @tomcheaney9

  13. #13
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    Quote Originally Posted by Uffdaphil View Post
    The .308 CMR I.D. is 1.25” and Sentry 7 is 1.40” so no go. As for the RE, I’m going to get more input on the Creed forum before I commit. I’ll post pics when finished. Probably after next quarter’s dividend at least.

    Thanks all for the clarifying info.
    Heh, I was sitting here eyeballing one, and thought it was bigger than 1.25" Too bad, I really like CMR's too.

  14. #14
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    Gawd I wish manufacturers were clearer about their .308 components. I like the Magpul SR25 tube because of the ten position holes. This is the site info: Due to its longer length, this receiver extension is compatible with most DPMS® Gen 1 pattern 7.62x51 firearms with standard length AR15/M4 carbine buffer components as well as aftermarket A5 buffers and springs for use on 5.56x45 AR15/M4 platforms.*

    I take this to mean for a .308 I use the shorter AR carbine spring (Sprinco Blue size) and AR15 buffer or can use the same tube for a 5.56 using the A5 spring (Sprinco green) and longer buffer. Is my understanding correct? Seems counter-intuitive to me to accomodate two different size springs in the same tube for different platforms. My brain is cramping.
    “What in the world is a moderate interpretation of a constitutional text? Halfway between what it says and what we'd like it to say?" -Antonin Scalia

  15. #15
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    Quote Originally Posted by Uffdaphil View Post
    The .308 CMR I.D. is 1.25” and Sentry 7 is 1.40” so no go. As for the RE, I’m going to get more input on the Creed forum before I commit. I’ll post pics when finished. Probably after next quarter’s dividend at least.

    Thanks all for the clarifying info.


    And I do think the Sentry will fit. Your measurements are not wrong, but your not looking at them the right way.

    Remember everything sits centered around the barrel or should be close to it. The CMR is 1.25" in DIA and and GB is 1.40" TALL.

    So lets break the measurements down:

    So since the GB sits on barrel that is in the center of rail you need to basically divide rail and barrel in half and figure out how much the GB sits above barrel. According to SLRs drawing its .477". Half of a .750 barrel is .3750", and the rail is .6250".

    Now add barrel half to GB above barrel height. .375+.477= .852 yeah I realize that this is more than half of rail measurement. But inside of rail is not just round. look at your other CMRs. There is a notch that runs along top rail to allow clearance for gas tube and gas block.

    So after all that just know a SLR Sentry 7 will fit CMR. Here is an example:
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    "And now you understand. Anything goes wrong, anything at all... your fault, my fault, nobody's fault... it won't matter - I'm gonna blow your head off. No matter what else happens, no matter who gets killed I'm gonna blow your head off." -Big Jake

    "All the Gods, all the heavens, all the hells, are within you." -Joseph Campbell

    Instagram- @tomcheaney9

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