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Thread: Army looking at a new 6.8mm round?

  1. #11
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    Quote Originally Posted by pinzgauer View Post
    If you look at the deaired max recoil and ammo weight profile combined with the performance expectations down range it's pretty clear that a 6.5 projectile will be a sweet spot for carbines.

    Especially when vest penetration (requiring velocity) , BC, sectional density is factored in.

    I expect we'll see 90-115g projectiles, lead free, etc. 6.5mm is the sweet spot for those.

    This also applies to comments in the other thread on creedmore about adoption of 6.8 spc. My prediction: ain't gonna happen. (Or Grendel, or any other non-caseless breakthrough)

    Just too many compromises (capacity, weight) with the offsetting improvements1 not solving perceived critical problems at hand. (Talking about big army priorities, I know all the advantages Grendel/spc offers. I'm sold. They are not, yet.)
    Sorry but SD doesn't mean jack unless the projectile is a solid and never changes shape. As soon as the bullet contacts something and the bullet changes shape that SD figure means nothing. Any caliber bullet can be made with the same BC using a /cal formula. The weight difference between a 6mm, 6.5 and 6.8 bullet with the same BC is only about 6-8gr. With a case the capacity of the Grendel or 6.8(36gr) the 6mm will have better exterior ballistics for long range but the 6.8 or 7mm will have better terminal performance considering bullets of identical construction.
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  2. #12
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    Quote Originally Posted by constructor View Post
    Sorry but SD doesn't mean jack unless the projectile is a solid and never changes shape. As soon as the bullet contacts something and the bullet changes shape that SD figure means nothing. Any caliber bullet can be made with the same BC using a /cal formula. The weight difference between a 6mm, 6.5 and 6.8 bullet with the same BC is only about 6-8gr. With a case the capacity of the Grendel or 6.8(36gr) the 6mm will have better exterior ballistics for long range but the 6.8 or 7mm will have better terminal performance considering bullets of identical construction.
    That's basically the reason Murray said 7mm was there ideal infantry caliber, the difference in terminal performance.

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  3. #13
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    Quote Originally Posted by mig1nc View Post
    That's basically the reason Murray said 7mm was there ideal infantry caliber, the difference in terminal performance.

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    Right. We talked about it several times while I worked on his 7mm UIAC bolts but I just couldn't make myself like a 130-140gr bullet going slow.
    Art at SSA made a 97gr AP bullet for the 6.8 that would defeat LIV armor over 80% of the time at 100yds. It had a thick jacket that would come apart and do the damage if no armor was present and the core would do the damage if they were wearing armor. At that time it was the only bullet usable in a AR15 that would defeat LIV. A 97gr at 2950fps out of a 16" barrel is pretty impressive.
    Last edited by constructor; 05-12-18 at 13:39.
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  4. #14
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    Quote Originally Posted by constructor View Post
    Sorry but SD doesn't mean jack unless the projectile is a solid and never changes shape. As soon as the bullet contacts something and the bullet changes shape that SD figure means nothing. Any caliber bullet can be made with the same BC using a /cal formula. The weight difference between a 6mm, 6.5 and 6.8 bullet with the same BC is only about 6-8gr. With a case the capacity of the Grendel or 6.8(36gr) the 6mm will have better exterior ballistics for long range but the 6.8 or 7mm will have better terminal performance considering bullets of identical construction.
    Seem to have missed my point.

    Yes, any caliber has it's sweet spot for BC. And sectional density is not the only factor in penetration (but it is a factor). And yes, SD only matters if it does not flatten/fragment (pay much attention to mainstream issue ammo lately?)

    It's just that for 6.5, that sweet spot is close to the sweet spot for the combination of carbine recoil, flat trajectory, and downrange energy. With decent penetration, especially with (the probably required) lead free projectiles.

    That "only 6-8 grains" difference is tangible performance difference when you are trying to optimize for a carbine with a particular weight/recoil profile while keeping downrange performance.

    The USSOCOM update a few posts back is worth a scan. Nary a mention of 6.8 and 7mm, yet several 6.5mm references and not just about creedmore.

    I'm a hardcore 7mm advocate for hunting, and used to compete IHMSA with a 7BR pistol. Love the 270. Still hunt with a 308, especially now that I can get decent BC bullets at lighter weight with excellent performance (TTSX).

    But when constrained to the recoil/trajectory/ammo weight envelope they (big Army) are working with, it means lighter bullets.

    The 6.8 bullet you mentioned with great vest/armor penetration sounds great, but normally sub-100g 6.8 projectiles are getting far out of the sweet spot for BC/trajectory and associated longer range performance (even accounting for lead free designs).

    I know you are a hardcore 6.8 SPC advocate on your commercial site, but I personally do not believe big Army will adopt SPC or Grendel, or any other intermediate with brass case (7x46, 6x40) short of caseless that has a breakthrough which improves ballistic performance without compromising weight/ammo loadout & recoil to do so.

    I'm a fan of the intermediate cartridge concept, but the logistical challenge and tradeoffs (15-20% less rounds for same weight) are just to big.

    Especially with the improved performance they are apparently seeing with the new 77g and 855A1 5.56 loadings. Which buys them time to develop/push caseless/poly case.
    Last edited by pinzgauer; 05-12-18 at 19:28.

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    Quote Originally Posted by pinzgauer View Post
    Seem to have missed my point.

    Yes, any caliber has it's sweet spot for BC. And sectional density is not the only factor in penetration (but it is a factor). And yes, SD only matters if it does not flatten/fragment (pay much attention to mainstream issue ammo lately?)

    It's just that for 6.5, that sweet spot is close to the sweet spot for the combination of carbine recoil, flat trajectory, and downrange energy. With decent penetration, especially with (the probably required) lead free projectiles.

    That "only 6-8 grains" difference is tangible performance difference when you are trying to optimize for a carbine with a particular weight/recoil profile while keeping downrange performance.

    The USSOCOM update a few posts back is worth a scan. Nary a mention of 6.8 and 7mm, yet several 6.5mm references and not just about creedmore.

    I'm a hardcore 7mm advocate for hunting, and used to compete IHMSA with a 7BR pistol. Love the 270. Still hunt with a 308, especially now that I can get decent BC bullets at lighter weight with excellent performance (TTSX).

    But when constrained to the recoil/trajectory/ammo weight envelope they (big Army) are working with, it means lighter bullets.

    The 6.8 bullet you mentioned with great vest/armor penetration sounds great, but normally sub-100g 6.8 projectiles are getting far out of the sweet spot for BC/trajectory and associated longer range performance (even accounting for lead free designs).

    I know you are a hardcore 6.8 SPC advocate on your commercial site, but I personally do not believe big Army will adopt SPC or Grendel, or any other intermediate with brass case (7x46, 6x40) short of caseless that has a breakthrough which improves ballistic performance without compromising weight/ammo loadout & recoil to do so.

    I'm a fan of the intermediate cartridge concept, but the logistical challenge and tradeoffs (15-20% less rounds for same weight) are just to big.

    Especially with the improved performance they are apparently seeing with the new 77g and 855A1 5.56 loadings. Which buys them time to develop/push caseless/poly case.
    I'm sure they will not adopt the Grendel or 6.8 but possibly LSAT or something with one of those calibers.
    The velocity of that 97gr AP is why it worked. With a case of 36gr capacity they needed a lighter bullet to get the velocity up even at 58000psi. A 123 going 2450 would never defeat LIV regardless of what it is made from. A 123 out of a long barrel Creedmoor at 2800 may work but no one we know of has ever developed a 6.5AP that will defeat LIV. If they decide to go with a 260 or Creed for sniper rifles they may.
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  6. #16
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    Quote Originally Posted by pinzgauer View Post
    Seem to have missed my point.

    Yes, any caliber has it's sweet spot for BC. And sectional density is not the only factor in penetration (but it is a factor). And yes, SD only matters if it does not flatten/fragment (pay much attention to mainstream issue ammo lately?)

    It's just that for 6.5, that sweet spot is close to the sweet spot for the combination of carbine recoil, flat trajectory, and downrange energy. With decent penetration, especially with (the probably required) lead free projectiles.

    That "only 6-8 grains" difference is tangible performance difference when you are trying to optimize for a carbine with a particular weight/recoil profile while keeping downrange performance.

    The USSOCOM update a few posts back is worth a scan. Nary a mention of 6.8 and 7mm, yet several 6.5mm references and not just about creedmore.

    I'm a hardcore 7mm advocate for hunting, and used to compete IHMSA with a 7BR pistol. Love the 270. Still hunt with a 308, especially now that I can get decent BC bullets at lighter weight with excellent performance (TTSX).

    But when constrained to the recoil/trajectory/ammo weight envelope they (big Army) are working with, it means lighter bullets.

    The 6.8 bullet you mentioned with great vest/armor penetration sounds great, but normally sub-100g 6.8 projectiles are getting far out of the sweet spot for BC/trajectory and associated longer range performance (even accounting for lead free designs).

    I know you are a hardcore 6.8 SPC advocate on your commercial site, but I personally do not believe big Army will adopt SPC or Grendel, or any other intermediate with brass case (7x46, 6x40) short of caseless that has a breakthrough which improves ballistic performance without compromising weight/ammo loadout & recoil to do so.

    I'm a fan of the intermediate cartridge concept, but the logistical challenge and tradeoffs (15-20% less rounds for same weight) are just to big.

    Especially with the improved performance they are apparently seeing with the new 77g and 855A1 5.56 loadings. Which buys them time to develop/push caseless/poly case.
    Above you said the 90-115 is a sweet spot so I gave you a 97gr AP then you say that is too light. You Grendel guys make it sound like a 123gr 6.5 is perfect but anything close is bad if it isn't a 6.5. It's been going on for 12 years on barfcom. We are all working off data of 2 cartridges that exist. A 6.8 will propel a bullet that is 8-10gr heavier the same vel as a 6.5 that is lighter out of the same length barrel. A heavier 6.8 bullet with the same BC at the same velocity will have the same trajectory but more energy.
    The 2 cartridges are much closer than the Grendel crowd wants to admit. If the military were to consider either the 6.5 or 6.8 the strength of the bolts and cases make the 6.8 case a better choice. There are way too many photos of broken Grendel bolts and swelled cases for that cartridge to be reliable for combat use.

    I'm sure they will not adopt the Grendel or 6.8 but possibly LSAT or something with one of those calibers.
    The velocity of that 97gr AP is why it worked. With a case of 36gr capacity they needed a lighter bullet to get the velocity up even at 58000psi. A 123 going 2450 would never defeat LIV regardless of what it is made from. A 123 out of a long barrel Creedmoor at 2800 may work but no one we know of has ever developed a 6.5AP that will defeat LIV. If they decide to go with a 260 or Creed for sniper rifles they may.
    Last edited by constructor; 05-14-18 at 08:22.
    AR15performance 68forums
    The 6.8 is the best choice for hunting deer and hogs with an AR15.

  7. #17
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    Quote Originally Posted by constructor View Post
    Above you said the 90-115 is a sweet spot so I gave you a 97gr AP then you say that is too light. You Grendel guys make it sound like a 123gr 6.5 is perfect but anything close is bad if it isn't a 6.5. It's been going on for 12 years on barfcom. We are all working off data of 2 cartridges that exist. A 6.8 will propel a bullet that is 8-10gr heavier the same vel as a 6.5 that is lighter out of the same length barrel. A heavier 6.8 bullet with the same BC at the same velocity will have the same trajectory but more energy.
    The 2 cartridges are much closer than the Grendel crowd wants to admit. If the military were to consider either the 6.5 or 6.8 the strength of the bolts and cases make the 6.8 case a better choice. There are way too many photos of broken Grendel bolts and swelled cases for that cartridge to be reliable for combat use.

    I'm sure they will not adopt the Grendel or 6.8 but possibly LSAT or something with one of those calibers.
    The velocity of that 97gr AP is why it worked. With a case of 36gr capacity they needed a lighter bullet to get the velocity up even at 58000psi. A 123 going 2450 would never defeat LIV regardless of what it is made from. A 123 out of a long barrel Creedmoor at 2800 may work but no one we know of has ever developed a 6.5AP that will defeat LIV. If they decide to go with a 260 or Creed for sniper rifles they may.
    It's not that it's too light, it's too stubby in 6.8, poorer BC to meet the overall parameters.

    Grendel is not even relevant to the point I was making. But even Bill Alexander has pointed out that the 95-115g range is the stronger performance area for Grendel.

    It's almost an accident of availability that the 120-123g 6.5 bullets became so popular in Grendel. I wish instead of making the 123g 6.5 amax and sst that Hornady did it at 115g. (Though I think 120-123g was the right call for an AR oriented 6.8 projectile).

    I don't give a rat's ass about barfcom debates, just was pointing out that if you look at the parameters big army is trying to meet, odds are that they will end up with 6.5 projectiles IF they commit to move away from 5.56. And most likely in some LSAT config. But that's a big IF.

    The performance envelope/profile they need/want to hit:

    - Same or less weight for std carbine loadout: 180 rounds + loaded carbine (SPC and Grendel are both 15-20% over this for same ammo loadout)

    - Reasonably flat trajectory out to 300, and ideally further. Reasonable meaning battle sight'ish, no crazy hold overs for 300m. 5.56 is the baseline, but current Grendel and especially SPC loadings being borderline.

    - improved 300m+ performance over 5.56 (lethality, penetration). Implies higher velocity than most current 5.56 and even SPC/Grendel loadings

    - reasonable recoil impulse given carbine weighing similar to current M4. Upper boundary being less that 7.62 NATO in light carbines. Probably in the same range or slightly higher than current SPC/Grendel in M4s.

    When you factor in those constraints, many reasonable sounding cartridges and even projectiles are not viable.

  8. #18
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    Quote Originally Posted by pinzgauer View Post
    It's not that it's too light, it's too stubby in 6.8, poorer BC to meet the overall parameters.

    Grendel is not even relevant to the point I was making. But even Bill Alexander has pointed out that the 95-115g range is the stronger performance area for Grendel.

    It's almost an accident of availability that the 120-123g 6.5 bullets became so popular in Grendel. I wish instead of making the 123g 6.5 amax and sst that Hornady did it at 115g. (Though I think 120-123g was the right call for an AR oriented 6.8 projectile).

    I don't give a rat's ass about barfcom debates, just was pointing out that if you look at the parameters big army is trying to meet, odds are that they will end up with 6.5 projectiles IF they commit to move away from 5.56. And most likely in some LSAT config. But that's a big IF.

    The performance envelope/profile they need/want to hit:

    - Same or less weight for std carbine loadout: 180 rounds + loaded carbine (SPC and Grendel are both 15-20% over this for same ammo loadout)

    - Reasonably flat trajectory out to 300, and ideally further. Reasonable meaning battle sight'ish, no crazy hold overs for 300m. 5.56 is the baseline, but current Grendel and especially SPC loadings being borderline.

    - improved 300m+ performance over 5.56 (lethality, penetration). Implies higher velocity than most current 5.56 and even SPC/Grendel loadings

    - reasonable recoil impulse given carbine weighing similar to current M4. Upper boundary being less that 7.62 NATO in light carbines. Probably in the same range or slightly higher than current SPC/Grendel in M4s.

    When you factor in those constraints, many reasonable sounding cartridges and even projectiles are not viable.
    I think you missed my point. There isn't that much difference in a 6.5 and 6.8 bullet. A 6.5 and a 6.8 bullet can be made with the same BCs and under 10gr difference. The difference in weight and velocity is offset by the bore area being able to create more force and overcome the weight. Think of the difference in diameters of hydraulic rams and capacity rating. A 6.8 with less case capacity can push a 130 Berger as fast as a Grendel can push a 123gr bullet. A 97gr copper and Tungsten bullet is as long as a 115 and I believe the BC was over .400. The mistake most people make is comparing existing bullets on the market. There are lots of match bullets for the 6.5 and lots of hunting bullets for the 6.8. The military will not use either, they will design their own. If we assume the smaller diameter bullet is always better a .257 would be a better choice for saving weight. Higher BCs, less weight more velocity. or Maybe a 6mm or a 224...Valkyrie. You don't think with Federal/ ATK having the biggest "IN" you could possibly have that maybe them dropping the Valkyrie on the market may be a hint? Saying they may be trying to show the military what a larger 224 can do like the Russian 7N6 but better.
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  9. #19
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    You also have to look at this in terms of carbine length barrels.

    Suppressors are also becoming more mainstream in the military.

    Since the US Army will likely never adopt bullpup rifles, swept volume will have to be a significant consideration.

    .224 Valkyrie wouldn't be a great fit, but I understand why it's mentioned.

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    I think 224 Valk would be a great SAW cartridge. On a 249 style weapon you dont mind a little longer barrel length, and plunging fire on a distance target would be greatly improved over a a similar 556 gun. The higher velocity and BC would mean 308+ reach in a very light platform. (something we desperaetly wanted in Afghanistan)

    Of course I believe the 249 is a poor weapon system and should be replaced sometime soon. The relibability just isnt there, and there is definetely weight to be cut from the over al package. Something like the Ares MCR in 224 valk would be the business.

    For carbines though, I dont think you could do much better than a 6.8 caliber with a M855A1 style bullet. Im sure if a little attention was left in the BC department: a 500 meter devastator could be a reality.
    Last edited by turnburglar; 05-21-18 at 17:50.
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