5.56 Hybrid case @ 80k PSi.

[LRRPF52]

I forgot a few companies, used to sell AR 15 uppers in 223 WSSM, and others, but they may not have been fast twist barrels.
Probably for varmints....plus WSSM cases have disappeared from the market.

Olympic Arms, then D-TECH made the WSSM uppers. The coolest WSSM is the 25, but COL is limited. You really need a new receiver set, not just the upper. They made an upper with a larger ID tunnel for the extension, but used standard AR lowers with their own single-stack mag.

WSSM is a non-starter even for Snipers and DMs due to mag capacity limits, but a freaking lightning bolt killer for hunting with the AR-15.

.224” bores are just too little bore volume to try to force more case capacity through. The returns are very diminishing for large back-end increases and throat/bore life is toast.

 

[Cascade Hemi]

D-TECH made the WSSM uppers. The coolest WSSM is the 25, but COL is limited. You really need a new receiver set, not just the upper. They made an upper with a larger ID tunnel for the extension, but used standard AR lowers with their own single-stack mag.

WSSM is a non-starter even for Snipers and DMs due to mag capacity limits, but a freaking lightning bolt killer for hunting with the AR-15.

.224” bores are just too little bore volume to try to force more case capacity through. The returns are very diminishing for large back-end increases and throat/bore life is toast.

The 6.8 extended receiver set and Mapull magazines (designed for Grendel) with Mutant x39 bolt makes a lot of sense. Grendel from a slightly longer AR loaded to 60K.

 

[SigSauerM7]

View attachment 8491775

The 6.8 extended receiver set and Mapull magazines (designed for Grendel) with Mutant x39 bolt makes a lot of sense. Grendel from a slightly longer AR loaded to 60K.

The Grendal casing has a slight taper like 7.62x39.

I always thought that the SPC "casing" was a great profile for M4 mags, but you cannot stuff 108 and 103 gr pills into it without dipping into the powder.

The SSA 140gr 6.8 SpC load basically gave you good numbers on paper..but it wasn't that Accurate overall. Maybe the ammo was a little heavy too.

The 6.8 extended reciever would be great for .257/5.56, 6mm/5.56, and some other rounds like 6mm SPC.

JSOC people on youtube keep saying that MK262 is enough. Is the juice worth the squeeze?

 

[Cascade Hemi]

Grendel has less taper than x39.

 

[SigSauerM7]

Grendel has less taper than x39.

Too much taper.

6.5x39 belongs in 6.1 lb Chinese 1.5 MOA AKM's. NP-103s.

 

[LRRPF52]

The 6.8 extended receiver set and Mapull magazines (designed for Grendel) with Mutant x39 bolt makes a lot of sense. Grendel from a slightly longer AR loaded to 60K.

I have a New Frontier Armory C-6.8 Receiver Set and Magpul Six8 20 and 30rd PMAGs to experiment with.

The Six8 PMAGs allow more COL, but the Geissele 6 ARC mags allow even more without any special receiver set, so....

I have samples of both, and the Geissele 6 ARC mags have a raw internal max length of 2.327”. Six8 PMAGs are more in the 2.310” length if I recall. I just measured them both a few days ago.

Six8 mags require slightly larger mag pouches to work, which isn’t a problem for me as I’ve been making mag pouches for 30 years from scratch.

I’m thinking of just throwing together a .224 Valkyrie build off the Six8 set and mags to show how even the best, longest .224” VLD projectiles perform at distance compared to 6.5mm. They don’t make much noise when they impact the steel even at 400-600yds in full value wind conditions, let alone 1000yds.

A receiver set that allows correct placement of the new .257” VLD bullets without intruding into the powder column, and a COL of 2.500” with relatively-compact magazines would make an ideal DMR/Light Sniper System. Performance would be between 6.5 Grendel and 6.5 Creedmoor, so rather marginal in the grand scheme of the bigger picture.

If you used an AerMet bolt and extension in 6.5 Grendel, you would add maybe 200fps mv. You start to see how trigger time and experience matter so much more, but it is important for the industry to keep pushing the edge on incremental improvements in case, propellant, bullet, and pressure containment system designs.

 

[LRRPF52]

The Grendal casing has a slight taper like 7.62x39.

I always thought that the SPC "casing" was a great profile for M4 mags, but you cannot stuff 108 and 103 gr pills into it without dipping into the powder.

The SSA 140gr 6.8 SpC load basically gave you good numbers on paper..but it wasn't that Accurate overall. Maybe the ammo was a little heavy too.

The 6.8 extended reciever would be great for .257/5.56, 6mm/5.56, and some other rounds like 6mm SPC.

JSOC people on youtube keep saying that MK262 is enough. Is the juice worth the squeeze?

7.62x39 has pretty extreme case taper, whereas Grendel doesn’t.

The SPC would have been great for military application in .257”, with mags that take longer COL, 30˚ shoulder, AerMet bolt or CNC liquid burnished bolt and extension, and higher BC projectiles in the 110-125gr region. It would not generate the same amount of “slap” on target within closer ranges that the .277” and .30 cals do, but killing performance would still be the same as any other medium bore 110-125gr, projectiles construction being more influential at that point.

The 130gr Berger Classic Hunter with .490 G1 BC/.251 G7 is where it’s at in the 6.8 if you’re wanting it to compare well with 6.5 Grendel. Load that in PRI or Six8 mags as long as you can and use the same powders known to perform in Grendel, and it’s a great intermediate-to-long range load, provided you have tighter twist.

The DoD entities who drove what became 6mm ARC were looking for long range performance over the 77gr, so Mk.262 has always had its limits. They just got tired of dealing with all the penalties of the SR-25/7.62 NATO weight/bulk/limited mag stowage, recoil, and muzzle blast.

They actually ran through the initial test iterations with 12-18” Grendels, and said for every shooting scenario they employed them in, there wasn’t a single instance where they would have preferred SR-25s. Hornady then said they could tweak it to make it better, and necked it down to 6mm. It would have been easier to dust-off 90-110gr class of bullets and optimize the BCs on them like they just did with the 100gr ELD-VT 6.5mm.

If you shoot 77gr even from 24” bolt guns next to a 12” Grendel on the same targets at distance, you quickly see that the juice is worth the squeeze. 77gr barely nicks the paint, whereas you see the typical bullet splash and base dirt/mud linear base-of-target splash from 6.5mm.

 

[SigSauerM7]

7.62x39 has pretty extreme case taper, whereas Grendel doesn’t.

The SPC would have been great for military application in .257”, with mags that take longer COL, 30˚ shoulder, AerMet bolt or CNC liquid burnished bolt and extension, and higher BC projectiles in the 110-125gr region. It would not generate the same amount of “slap” on target within closer ranges that the .277” and .30 cals do, but killing performance would still be the same as any other medium bore 110-125gr, projectiles construction being more influential at that point.

The 130gr Berger Classic Hunter with .490 G1 BC/.251 G7 is where it’s at in the 6.8 if you’re wanting it to compare well with 6.5 Grendel. Load that in PRI or Six8 mags as long as you can and use the same powders known to perform in Grendel, and it’s a great intermediate-to-long range load, provided you have tighter twist.

The DoD entities who drove what became 6mm ARC were looking for long range performance over the 77gr, so Mk.262 has always had its limits. They just got tired of dealing with all the penalties of the SR-25/7.62 NATO weight/bulk/limited mag stowage, recoil, and muzzle blast.

They actually ran through the initial test iterations with 12-18” Grendels, and said for every shooting scenario they employed them in, there wasn’t a single instance where they would have preferred SR-25s. Hornady then said they could tweak it to make it better, and necked it down to 6mm. It would have been easier to dust-off 90-110gr class of bullets and optimize the BCs on them like they just did with the 100gr ELD-VT 6.5mm.

If you shoot 77gr even from 24” bolt guns next to a 12” Grendel on the same targets at distance, you quickly see that the juice is worth the squeeze. 77gr barely nicks the paint, whereas you see the typical bullet splash and base dirt/mud linear base-of-target splash from 6.5mm.

7.62x39 has pretty extreme case taper, whereas Grendel doesn’t.

The SPC would have been great for military application in .257”, with mags that take longer COL, 30˚ shoulder, AerMet bolt or CNC liquid burnished bolt and extension, and higher BC projectiles in the 110-125gr region. It would not generate the same amount of “slap” on target within closer ranges that the .277” and .30 cals do, but killing performance would still be the same as any other medium bore 110-125gr, projectiles construction being more influential at that point.

The 130gr Berger Classic Hunter with .490 G1 BC/.251 G7 is where it’s at in the 6.8 if you’re wanting it to compare well with 6.5 Grendel. Load that in PRI or Six8 mags as long as you can and use the same powders known to perform in Grendel, and it’s a great intermediate-to-long range load, provided you have tighter twist.

The DoD entities who drove what became 6mm ARC were looking for long range performance over the 77gr, so Mk.262 has always had its limits. They just got tired of dealing with all the penalties of the SR-25/7.62 NATO weight/bulk/limited mag stowage, recoil, and muzzle blast.

They actually ran through the initial test iterations with 12-18” Grendels, and said for every shooting scenario they employed them in, there wasn’t a single instance where they would have preferred SR-25s. Hornady then said they could tweak it to make it better, and necked it down to 6mm. It would have been easier to dust-off 90-110gr class of bullets and optimize the BCs on them like they just did with the 100gr ELD-VT 6.5mm.

If you shoot 77gr even from 24” bolt guns next to a 12” Grendel on the same targets at distance, you quickly see that the juice is worth the squeeze. 77gr barely nicks the paint, whereas you see the typical bullet splash and base dirt/mud linear base-of-target splash from 6.5mm.

This is what my brain has been thinking for a long time more or less.

The M4A3 is the future.

 

[LRRPF52]

For general issue, we need to be thinking about getting the carbine smaller and streamlining the ancillary systems.

Bolt-on boxes with independent batteries and cables all over is a colossal abortion in and around any type of snag hazard environment (the woods, in and out of vehicles, clearing corners and doorways, getting in and out of barricades/loopholes, and just daily carry). I hate boxes all over that ruin the natural pointability of the Colt Commando variants, but their capabilities are a baseline expectation for any modern Carbine.

Coming from the Aerospace and 11B worlds, I’m looking at it how we would approach the weight/balance/CofG/performance/space trade-offs and demanding that I have my 11B Caveman solutions with my Aerospace materials science and integrated systems architecture in the same bowl.

This is what I’ve been working on for the past 20 years basically, with the caveat that if the right people aren’t involved, it will never make it. Gotta have only A players in that game.

The kinetic aspects of the basic firearm, namely internal/external/terminal ballistics are only one aspect of it.

The Integrated Systems is the real hard nut to crack, and only really exists at the cutting edge in military aerospace.

The civilian sector iterations of things like iPhone, VHSC, CFD, materials science, additive mfg, etc. are trickle-down technologies from DoD that they allowed out of the National Labs and other communities in that space.

Systems engineers and various technicians are typically employed in the Aerospace world, not firearms, but the ancillary systems evolutions since JSOC started mounting LAMs and WPLs to carbines requires AeroE level involvement to do what I see as the next generation moving forward.

We saw a lot of these challenges in Land Warrior and I haven’t seen much of anything done about it to solve them. Given the nature of the culture within DoD for small arms, that should be no surprise to anyone.

 

[LRRPF52]

The KAC PDW was one of the coolest evolutions of the Stoner family of weapons in 6x35mm (.221 Fireball necked-up).

Look at how small the mags are. You could carry impressive basic loads (300-600rds) and not think much about it.

Hand that to Weapons Squad AGs/ABs, Mortars, 1SGs, PSGs, COs, XOs, JTACs, K-9 Handlers, Grenadiers with a 7-9” barrel 40mm underneath it, RTOs, FOs, Combat Medics, etc.

That’s what we need to be thinking about vs the 14lb NGSW-R boat anchor.

Have Riflemen and LMGs with an Intermediate cartridge in .257” or 6.5mm that has higher BC/SD for reaching out with same or better supersonic reach as 7.62 NATO, but high round count carrying capacity, low recoil.

Go 12” for the Carbine, suppressed, lightweight.

The XM7 is an offense, as are any AR-10 sized offerings. They’re bad enough before you even configure them with optics, LAMs, slings, and pressure switches.

 

[putput30]

The KAC PDW always had a place in my heart. Unfortunate that nothing really became of it. I also found that the .257 caliber in the 115-130 class would probably be the ideal do all caliber.

 

[LRRPF52]

The KAC PDW always had a place in my heart. Unfortunate that nothing really became of it. I also found that the .257 caliber in the 115-130 class would probably be the ideal do all caliber.

Imagine the KAC LMG in something like 6.5 Grendel or a .257” Intermediate cartridge spitting 115-130gr, with very low recoil.

That allows you to ditch the 7.62 NATO and lighten everything across the board, from weapon weight to ammo, in smaller footprints across the logistics chain from the pallets down to pouches and nutsacks in the guns.

Instead, these guys conceived of heavier weapons with heavier ammo, pushing alloy capabilities in pressure containment, for an organization that can’t maintain the current weapons properly due to skills gap.

 

[SigSauerM7]

Imagine the KAC LMG in something like 6.5 Grendel or a .257” Intermediate cartridge spitting 115-130gr, with very low recoil.

That allows you to ditch the 7.62 NATO and lighten everything across the board, from weapon weight to ammo, in smaller footprints across the logistics chain from the pallets down to pouches and nutsacks in the guns.

Instead, these guys conceived of heavier weapons with heavier ammo, pushing alloy capabilities in pressure containment, for an organization that can’t maintain the current weapons properly due to skills gap.

When engagements get past 500-600 yards, 11 are pulling out .300 Win Mags, .338 Lapua and .50 BMGs.

Imagine the KAC LMG in something like 6.5 Grendel or a .257” Intermediate cartridge spitting 115-130gr, with very low recoil.

That allows you to ditch the 7.62 NATO and lighten everything across the board, from weapon weight to ammo, in smaller footprints across the logistics chain from the pallets down to pouches and nutsacks in the guns.

Instead, these guys conceived of heavier weapons with heavier ammo, pushing alloy capabilities in pressure containment, for an organization that can’t maintain the current weapons properly due to skills gap.

Imagine the KAC LMG in something like 6.5 Grendel or a .257” Intermediate cartridge spitting 115-130gr, with very low recoil.

That allows you to ditch the 7.62 NATO and lighten everything across the board, from weapon weight to ammo, in smaller footprints across the logistics chain from the pallets down to pouches and nutsacks in the guns.

Instead, these guys conceived of heavier weapons with heavier ammo, pushing alloy capabilities in pressure containment, for an organization that can’t maintain the current weapons properly due to skills gap.

I feel like fire teams still need M855 or M855A1 @ 1200 RPM to keep heads down and flank your ass off.

550 RPM KAC in 6.5 Creedmoor or M80A1 like the Rangers have been messing with seems slow.

I guess it depends on your battle order.

The KAC LMG in 6.5 CM ball has a HUGE Capability.

 

[LRRPF52]

500-600yds is literally child’s play for Grendel from short barrels in the 10.5” to 12” lengths. My small kids make 1st-round hits with 12” Grendel on 2 MOA steel plates at those ranges.

1200rpm? We don’t have any MGs that run those cyclic rates. You burn through ammo very quickly with 1200rpm. There’s a reason why the Germans had 9-man MG34 and MG42 Gun Squads with only 1 Machinegunner. They also used horses and motorcycles with the side cars to carry additional ammo cans, spare barrels, and the Lafette tripod. Those are GPMGs for Platoon and Company-support, not LMGs in the Rifle Squad, so a big difference.

The slower cyclic rate of constant-recoil operating systems allows you to put continuous fire on movers very easily, and the gun doesn’t exhibit muzzle climb. Training and proficiency with constant-recoil systems is very fast, very easy. It feels like you can write your name with them. The KAC LAMG is constant-recoil.

High Performance Intermediate cartridges are where it’s at, not full-size legacy cartridges. You can duplicate 6.5CM trajectory with maybe 60% of its recoil, and 68-72% of its weight.

 

[SigSauerM7]

500-600yds is literally child’s play for Grendel from short barrels in the 10.5” to 12” lengths. My small kids make 1st-round hits with 12” Grendel on 2 MOA steel plates at those ranges.

1200rpm? We don’t have any MGs that run those cyclic rates. You burn through ammo very quickly with 1200rpm. There’s a reason why the Germans had 9-man MG34 and MG42 Gun Squads with only 1 Machinegunner. They also used horses and motorcycles with the side cars to carry additional ammo cans, spare barrels, and the Lafette tripod. Those are GPMGs for Platoon and Company-support, not LMGs in the Rifle Squad, so a big difference.

The slower cyclic rate of constant-recoil operating systems allows you to put continuous fire on movers very easily, and the gun doesn’t exhibit muzzle climb. Training and proficiency with constant-recoil systems is very fast, very easy. It feels like you can write your name with them. The KAC LAMG is constant-recoil.

High Performance Intermediate cartridges are where it’s at, not full-size legacy cartridges. You can duplicate 6.5CM trajectory with maybe 60% of its recoil, and 68-72% of its weight.

Nice.

Canadians C9s are full motherfucker gas @ 1100-1200 rpm.

I was ranging out houses @ 1500 yards in my car today to simulate 6.5 CM KAC LMG.

That is WAY farther then 600 yards. Lol.



Duplicating 6.5 CM drop with less weight would be good. Hard to run outside when it's 95F with full humidity like Fort Benning or Ukraine.

Section fire based around MG42s was enough to take out everything. Even 600 Rangers at Anzio ambushed..

Troops panic under MASSIVE fire unless they are super experienced.

I recently saw images of 1945 Ukrainians/Russians in American Helmets and uniforms carrying MG42s and Burp guns on the roll kicking in German doors to nicely groomed gardens and houses full of women and kids.. Creepy..

Monkey see monkey do.

Anyways.


The goddamn KAC LMG is a good idea.

Get a bunch of those going. That would work good. Rangers like them.