The U.S. Army Is Developing a new 6.8-millimeter bullet.

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  • smdub

    Ultimate Member
    MDS Supporter
    Nov 14, 2012
    4,609
    MoCo
    You could push a hybrid case on the Grendel, with an exotic materials bolt and approached 6.8 x51 kinetic energy.

    Not even close. The 6.5 w/ 130gr from the same 16" barrel is ~2300fps. Nowhere in the ballpark of the 6.8x51 140gr 3000fps. Grendel is roughly HALF the energy. Grendel can't even use the same pressures as 5.56 due to bolt problems. It a dream to think you'd be able to double the pressure even with exotic materials.
     

    DavidA

    The Master of Disaster
    Dec 6, 2013
    355
    Annapolis
    Tool steel like Odin work bolts which I have , are made of case hardened 8620 steel which has a tensile strength of 820 yield strength of 590 mpa. I’ve used these on some rather hot loads ( 56,000 psi I would guess) and never had a bolt failure.

    Carpenter steel 158 bolts (Giesele enhanced bolts) have tensile of 1,120 mpa and yields of 1,000 mpa

    Steel nickel alloys can have Tensile of 1,490 mpa with 1,460 mpa yields. The problem with these alloys is machining the. Fan blades of jets are made of this type of steel, my father many years ago working for GE at the time developed chemical machining to machine the blades rough castings. So it can be done. But it is a little expensive to say this least . So if you increase strength by 75% an hybrid cartridge could work .

    Cartridge I was using for Grendel is a 123 gr bullet not a 130 gr as suggested. There are 16” barrels that get 2,470 out of Hornady 6.5 Grendel black ammo. Hand loads will exceed 2,500 fps. Which puts you right at 1,700 ft lbs. I don’t have a 16” but a 20” BHW I get around 2,570 fps out of 123’s . It is crazy how there is that much difference between barrel manufactures.

    Any hoot, for me the greatest fall back of the Grendel case is that the case head area is thin relative to say the 6.8 spc . This in turn lets the brass cold flow when fired with hot loads only get you 3 reloads before they are done. Primer pockets go.

    The just to finish up the SIG fury hybrid case has stirred the pot. Start up company called Shell Shock has started producing hybrid cases.

    So is 65,000 to 70,000 achievable in a 6.5 Grendel, AR15 package ? Looking at the pure numbers, yes. It will require bolts with more exotic materials and hybrid cases. But easily achievable with current available technology. Which is coming to market. The only thing holding it back are two things, customer demand and reluctance of the big players to start it , because it quickly makes current technology and tooling obsolete.

    Could one basically do it yourself? Yes but you would absorb a lot of development cost and time with no reasonable way to capture it. It is coming.


    Sent from my iPhone using Tapatalk
     

    Afrikeber

    Ultimate Member
    Jan 14, 2013
    6,577
    Urbana, Md.
    Tool steel like Odin work bolts which I have , are made of case hardened 8620 steel which has a tensile strength of 820 yield strength of 590 mpa. I’ve used these on some rather hot loads ( 56,000 psi I would guess) and never had a bolt failure.

    Carpenter steel 158 bolts (Giesele enhanced bolts) have tensile of 1,120 mpa and yields of 1,000 mpa

    Steel nickel alloys can have Tensile of 1,490 mpa with 1,460 mpa yields. The problem with these alloys is machining the. Fan blades of jets are made of this type of steel, my father many years ago working for GE at the time developed chemical machining to machine the blades rough castings. So it can be done. But it is a little expensive to say this least . So if you increase strength by 75% an hybrid cartridge could work .

    Cartridge I was using for Grendel is a 123 gr bullet not a 130 gr as suggested. There are 16” barrels that get 2,470 out of Hornady 6.5 Grendel black ammo. Hand loads will exceed 2,500 fps. Which puts you right at 1,700 ft lbs. I don’t have a 16” but a 20” BHW I get around 2,570 fps out of 123’s . It is crazy how there is that much difference between barrel manufactures.

    Any hoot, for me the greatest fall back of the Grendel case is that the case head area is thin relative to say the 6.8 spc . This in turn lets the brass cold flow when fired with hot loads only get you 3 reloads before they are done. Primer pockets go.

    The just to finish up the SIG fury hybrid case has stirred the pot. Start up company called Shell Shock has started producing hybrid cases.

    So is 65,000 to 70,000 achievable in a 6.5 Grendel, AR15 package ? Looking at the pure numbers, yes. It will require bolts with more exotic materials and hybrid cases. But easily achievable with current available technology. Which is coming to market. The only thing holding it back are two things, customer demand and reluctance of the big players to start it , because it quickly makes current technology and tooling obsolete.

    Could one basically do it yourself? Yes but you would absorb a lot of development cost and time with no reasonable way to capture it. It is coming.


    Sent from my iPhone using Tapatalk
    Excellent read.
     

    smdub

    Ultimate Member
    MDS Supporter
    Nov 14, 2012
    4,609
    MoCo
    Carpenter 158 is already the mil-spec for 5.56 bolts. You'd need roughly 100ksi case pressure for the Grendel to match the Fury. You'd need a steel that's twice the strength of C158. Would be much smarter to redesign the Grendel to use a rebated case so it could at least reach 5.56 SAAMI pressures to begin with.

    Just because you've never had a bolt failure means nothing. You are eating into the safety factor. Hand loads in the Fury could do the exact same thing. Same with hand load data using a lighter poorer BC bullet just to try and match muzzle energy. Apples to apples the Grendel and Fury will never be in the same league of capability. The case capacities and bolt strength differences due to physical size can't be overcome.

    Furry hybrid Sig brass is now on the market. This must be a wildcatters dream. Neck it down to 6.5 (PRC?) or up to 7mm to be able to use the available ultra high BC bullets that already exist and get a couple hundred more fps with the extra pressure.
     

    DavidA

    The Master of Disaster
    Dec 6, 2013
    355
    Annapolis
    Yes I have thought of that as well rebating the rim will solve a lot of issues. It would be better servers by redesigning case as a hybrid to over come bolt issues, but retain the basic casing dimensions.


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    DavidA

    The Master of Disaster
    Dec 6, 2013
    355
    Annapolis
    The point of this exercise is not to duplicate ballistics. The point is the Sig Fury is overkill. It weighs a ton and it limits ammo that can be carried. In any fire fight it does not mater if someone is close or far or is whether or not if they are wearing body armor. When you are out of ammo. Things go sideways quick


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    U.S.SFC_RET

    Ultimate Member
    Dec 8, 2005
    6,474
    Thats the limitation of the AR15, the bolt lug strength. We are already into special steels to get it to work with bigger case heads. I know there are some even more exotic steels possible but at what safety factor?

    I think the hybrid case will eventually be applied to other cartridges. Will give a few calibers a boost in performance or a new lease on life.

    6.8 Fury is partially about defeating body armor. Overmatch. I don't think the existing 6.5/6.8 AR15 cartridges get in done in that arena. The heavy bullets goinging slower are at a disadvantage.
    This round defeats body armor well past 600 meters.
     

    Docster

    Ultimate Member
    Jul 19, 2010
    9,757
    Um, where have you been for the last few years? old news. the round has already been developed.

    The round is called the 6.8 fury. Sig Sauer makes the rifle. Vortex makes the optics.
    Correct. The article is from 2019
     

    LeadSled1

    Ultimate Member
    MDS Supporter
    Apr 25, 2009
    4,221
    MD
    We outranged our adversaries in Iraq and Afghanistan which gave us a safer engagement distance. Near peer have our same current engagement range. We are trying to go further for better stand off and beneficial engagement range for us while still being able to defeat body armor.
     

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