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Thread: Building a 6.5 Grendel input

  1. #1
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    Building a 6.5 Grendel input

    Im wanting to put together a nice all around 6.5 Grendel rig for some range- distance and hunting. I've always purchased factory guns/uppers and then change up typical furniture/accessories but never piece together a "custom" rifle. I tend to steer away from Franken builds because of possible reliability issues etc but would with quality parts and help with my buddy (Sherriff's armour), I'm going to give it a whirl.

    Heres what I have together so far. Feel free to give me some input.

    LMT MARS-l lower receiver
    LMT m4 upper receiver
    LMT LPK
    LMT buffer tube and stock
    LMT carrier
    JP enterprises enhanced 6.5 Grendel Bolt
    JP enterprises H2 Silent Capture Buffer

    Giessele SD-E trigger
    Geissele URG Airborne CH
    Giessele MK16 13.5 rail (covers gas block)
    Geissele low pro gas block (rifle length)
    Proof Research 18" Carbon Fiber barrel (Rifle length gas)

    Sierra precision SPR Grip
    Harris 6-9" bipod

    Leupold Mark6 3-18x44 (already have)
    Giessele SOPMOD mk6 34mm mount (already have)

    Can a guy get 1/2 MOA out of a gas gun?






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  2. #2
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    You certainly have the barrel that should get you .5 MOA with match or hand loads. Sounds like an awesome build. Would like to see the final product.

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    My only (slight) regret in building a 18” Grendel upper is not going with a 20” barrel for a wee bit more velocity for longer range. Bill Alexander has said that he feels 18” is the best all-around length for the cartridge though. You’ve assembled a quality pile of components. In case you weren’t aware, the bolt you’ve selected is of the superior “Type II” I.e. 0.136” depth. This will aid in bolt strength and longevity as opposed to alternative 0.125” depth.

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    Quote Originally Posted by Gatorshark View Post
    You certainly have the barrel that should get you .5 MOA with match or hand loads. Sounds like an awesome build. Would like to see the final product.
    Thank you, there are a good handful of solid barrels to choose from but decided on Proof Research for weight and accuracy package. Trying to keep the rifle somewhat light for hunting hogs or deer but not necessarily a full lightweight build. Give and take here and there where I can. 1/2 moa is the goal!

    Quote Originally Posted by gunnerblue View Post
    My only (slight) regret in building a 18” Grendel upper is not going with a 20” barrel for a wee bit more velocity for longer range. Bill Alexander has said that he feels 18” is the best all-around length for the cartridge though. You’ve assembled a quality pile of components. In case you weren’t aware, the bolt you’ve selected is of the superior “Type II” I.e. 0.136” depth. This will aid in bolt strength and longevity as opposed to alternative 0.125” depth.
    I've teetered on 16, 18 or 20 inch. Proof only makes minimum 18" in 6.5 grendel anyways and exactly what you said with 18" being the consensus for all around solid length- especially for hunting rig. Im a little limited where I am with range. Nothing around over 500 yards unless I drive a few hours. I want to build a rifle that makes me essentially the deciding factor. I definitely read up about the bolt face issues with thinner walled bolt face as why I chose JP .136" bolt. I have their full BCG and Silent capture buffer in a recce setup and its just butter combo. Thanks for the reply!

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    Quote Originally Posted by gunnerblue View Post
    My only (slight) regret in building a 18” Grendel upper is not going with a 20” barrel for a wee bit more velocity for longer range. Bill Alexander has said that he feels 18” is the best all-around length for the cartridge though. You’ve assembled a quality pile of components. In case you weren’t aware, the bolt you’ve selected is of the superior “Type II” I.e. 0.136” depth. This will aid in bolt strength and longevity as opposed to alternative 0.125” depth.
    Actually The .136 recess bolts are 8% weaker than the .124 recess bolts as long as both bolts are made from the same material and have the same heat treat. Like Maxim, they make both bolts, same material and heat treat. You can walk into any engineers office and ask them to find the truth.
    Last edited by constructor; 01-23-20 at 20:34.

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    Quote Originally Posted by constructor View Post
    Actually The .136 recess bolts are 8% weaker than the .124 recess bolts as long as both bolts are made from the same material and have the same heat treat. Like Maxim, they make both bolts, same material and heat treat. You can walk into any engineers office and ask them to find the truth.
    Thank you for that. It is my understanding that the deeper depth allows for a stronger extractor design and that that is the advantage over the shorter depth.

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    Quote Originally Posted by gunnerblue View Post
    Thank you for that. It is my understanding that the deeper depth allows for a stronger extractor design and that that is the advantage over the shorter depth.
    I understand you have read that on the forums, the same 6 guys have been posting it since 2007 when I joined arfcom and Snipershide.

    The extractors are the same on the 7.62x39 and the Grendel. AA use to sell the machined 7.62x39 extractors marked as Grendel, same ones Rguns, AR15 Hardware sold and may still sell.
    Back in 2004 it wasn't as easy to have custom bolts made so they just used 5.56 bolts and opened up the face to accept the larger grendel case. The Lapua rim was thicker so the extractors would not snap over the rim so they had to make the bolt recess deeper at the same time they opened it up. That made the bolt weaker but they had to explain why they did it and they decided to cover it up/make it sound better without saying it made the bolt weaker. They should have machined the bolt from scratch and moved the extractor pivot pin forward .012". Of course they couldn't change from what they started with or they would have had to change their story.
    Notice on each side of the stiffener lug it is thicker, not dished like a normal 5.56 extractor. Attachment 60554
    Last edited by constructor; 01-24-20 at 17:00.

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    Quote Originally Posted by constructor View Post
    Actually The .136 recess bolts are 8% weaker than the .124 recess bolts as long as both bolts are made from the same material and have the same heat treat.
    This would be true if there also were not certain dimensional changes. But there ARE certain dimensional changes, so your "8% weaker" is only a guess. However, yes, a Grendel boltface with thinner walls and a deep boltface recess is weaker than a 5.56 bolt. This is obvious, and is one of the reasons Grendel average maximum chamber pressures are specced at 50,000 psi.

    Quote Originally Posted by constructor View Post
    The extractors are the same on the 7.62x39 and the Grendel.
    Yes. And? I think it's a good idea to strengthen Grendel and 7.62x39 extractors, since they're based on the same case. Don't you?

    Quote Originally Posted by constructor View Post
    Back in 2004 it wasn't as easy to have custom bolts made so they just used 5.56 bolts and opened up the face to accept the larger grendel case.
    Not sure if you're talking about Alexander Arms, specifically, or the world of 7.62x39 ARs. Alexander Arms contracted to have their Beowulf and Grendel bolts machined from scratch rather than reaming existing 5.56 bolts.

    Nobody in the history of the 6.5 Grendel, neither Bill Alexander nor its fan boys, have claimed a Grendel bolt is stronger than a 5.56 bolt. The claim was it was as a strong as it could be, given the constraints and the tradeoffs. For example, it's not necessarily a good idea to just move the extractor pin forward 0.012, because then the nose of the extractor is in danger of jutting out beyond the lugs.

    Do, I personally, believe existing Grendel bolts, like the ones I sell, are as strong as they CAN be? No. I think there's still room for small improvements. But that's a whole 'nuther thread.

  9. #9
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    One heck of a parts list for this build. Should come out nicely. I had an LMT MARS lower on my short list.
    ETC (SW/AW), USN (1998-2008)
    CVN-65, USS Enterprise

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    Quote Originally Posted by BluntForceTrauma View Post
    This would be true if there also were not certain dimensional changes. But there ARE certain dimensional changes, so your "8% weaker" is only a guess. However, yes, a Grendel boltface with thinner walls and a deep boltface recess is weaker than a 5.56 bolt. This is obvious, and is one of the reasons Grendel average maximum chamber pressures are specced at 50,000 psi.



    Yes. And? I think it's a good idea to strengthen Grendel and 7.62x39 extractors, since they're based on the same case. Don't you?



    Not sure if you're talking about Alexander Arms, specifically, or the world of 7.62x39 ARs. Alexander Arms contracted to have their Beowulf and Grendel bolts machined from scratch rather than reaming existing 5.56 bolts.

    Nobody in the history of the 6.5 Grendel, neither Bill Alexander nor its fan boys, have claimed a Grendel bolt is stronger than a 5.56 bolt. The claim was it was as a strong as it could be, given the constraints and the tradeoffs. For example, it's not necessarily a good idea to just move the extractor pin forward 0.012, because then the nose of the extractor is in danger of jutting out beyond the lugs.

    Do, I personally, believe existing Grendel bolts, like the ones I sell, are as strong as they CAN be? No. I think there's still room for small improvements. But that's a whole 'nuther thread.
    John, You guys have been telling everyone that will listen the Grendel bolts with the .136 recess are stronger/better bolts than the ones(264lbc or 7.62x39) with a .124 recess since 2007 on arfcom. LRRPFFTT posts all of those drawings that aren't to scale to prove it but they aren't to scale and are not correct. Tony Rumore(Tromix) has been trying to tell him for the past year or two also.
    I didn't say you said Grendel bolts are stronger than 5.56 bolts.
    Lets say Maxium makes .448 dia bolts with a .124 recess and .448 dia bolts with a .136 recess, his bolts with a .124 recess are stronger and ANY engineer can explain it. The bolts AA uses have no other dimensional changes from a mil spec bolt other than the face dia and recess. Anyone can measure the lug sizes and web thickness and tell there is no difference. Yes I still have a few from 2008, I do not have one from the first 6.5css that i bought in 2005, it had a .124 recess anyway.
    As for the"monster" bolts you sell... they seem to be nitride treated(made by Swann or millenium...Toolcraft?). IF they are the lugs will compress over time and headspace will increase. The first signs will be flattened primers, then blown primers. Checking the headspace with a no-go then field will tell. Measuring the lug length could expose the problem, they should be .277" long and I've seen some that have compressed close to .010". I predict a few years down the road there will be a crap load of problems related to these nitride treated bolts.
    The point I was making is for 12 years you guys have been telling everyone the .136 recess Grendel bolts are stronger and you have fooled a lot of people. In the beginning sure bolts made from 9310 were stronger than 8620 but now almost everyone is making all bolts from the same material and using the same heat treat.
    Anyone can figure it out if they just try, measure the lugs lxWxH, measure the recess, measure the web thickness. Length of lug minus the depth of recess= the amount of 100% attachment.

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