AR big bore caliber... from 6.8?

[JeeperCreeper]

I've been talking with friends about it since the 350 Legend was announced...

... But with the popularity of AR style rifles mixed with straight wall cartridges, I'm hoping for a new caliber war. From my 3 minutes of research, and hours of talking trash, it looks like a 6.8 SPC case can be blown out to a straight walled 10mm/.40

So with .450 Bushmaster (.45 extra long) and .350 Legend (9mm extra long), we could have a .40 extra long using 6.8 as the parent case.

From what I've been told, there's the .401 Self Loading from before WW1. It tossed a 200 grain pill around 2000 ftlbs of energy with 1.5" long case at 37,000 psi.

With a 6.8 at around 1.66" long and 55,000 psi, it would assume it's .40 offspring would be a tad above that .401 SL at over 2000ftlbs... Maybe 2300

And with 350 Legend at 1800ftlbs, and .450 Bushmaster at 2700ftlbs, it would slot right in between.

So.... Why would this cartridge be needed? It wouldn't. But it might sell... because why not? I have no skill in machining nor handloading, so I would never be able to "wildcat" it. I just thought I'd post what I've been thinking about while I'm on the commode.

What's a cool name? Maybe .400 Myth. Or 10mm Widsith. Yes, those are rip-offs of Legend and Beuwolf/Grendel because it's a rip-off caliber.

 

[someguy2800]

Starline sells 6.8 basic brass that is already straight wall. I swear I saw someone had already made exactly what you are talking about but I'll be darned if I can find it.

There is a 375 caliber wildcat called the 375 FUW. It was made by the same guy that invented the 357AR, so you might be able to derive what FUW stands for.

https://mdws.forumchitchat.com/post/375fuw-10182430?pid=1308964235

 

[gotboostvr]

It's an interesting idea I hadn't thought of. Plenty of good hard cast bullets already available, JHP's might take a little to catch up.

 

[.455_Hunter]

There is truly very little new under the sun in terms of cartridge development. The .350 Legend fanatics get twisted dainties when you point out that the chronograph velocities of the 180 gr factory load are within 100 fps of the chronograph velocities of the .351 Winchester, and that's with Legend having the advantage of a fixed breech bolt gun and the .351 having to operate it's semi-auto action. Your proposed cartridge would duplicate the .401 with a rimless case and not the cool hemispherical RN FMJ of the older round.

 

[Double Naught Spy]

Yes, those are rip-offs of Legend and Beuwolf/Grendel because it's a rip-off caliber.

These days, what isn't a ripoff caliber? For every caliber out there, you can find something close to it in performance. It will be slightly different in certain parameters that the designer will deem significantly important, but otherwise only slightly different.

 

[JeeperCreeper]

Yeah.... But marketing for AR platforms using existing bolt carrier groups and fill a role in a popular niche could be profitable.

Maybe Federal could try and save themselves from their .224 Valkyrie debacle... Or maybe they won't want to risk another 6.8 offspring.

Maybe Remington could try to compete against Winchester's Legend like the old days and see which one sticks around, but that means Remington would have to innovate... Kind of.

I dunno. Just shop talk, I guess.

If anyone comes out with one, I just wanna be able to raise my hand and say "I thought of that too!" like a little kid

 

[jmr40]

Energy numbers don't kill stuff. The 350 legend and 450 BM are designed for people living in states where hunters are handicapped by being forced to use straight walled cartridge cases. On deer size game I'd rather shoot one with one of the better 223 loads. On game bigger than deer I'd much rather shoot either the 6.5 Grendel or the 6.8 than either the 350 legend or 450 BM.

 

[mcb]

Kinetic energy is the only energy the bullet has when it gets to the target to do damage to the target.

I like the idea OP. I would be interested. I am tempted to start building a 350 Legend to go with my 450 Bushmaster. I hunt in a state that would let me hunt with bottleneck cartridges and yet I have hunted the past few season with straight-wall cartridges and the last two years with a 450 Bushmaster I built. A 40 cal straight wall cartridge would fit nicely into the very tiny niche between 450 BM and 350 Legend. It would probably not sell alot but it would sell, especially in those former slug only states that have become straight-wall only states. Magazines would be the only issue that would require any major engineering.

Theses straight-wall cartridges do have one advantage over the bottle neck cartridges and that is for sub-sonic use. When you're limited to 1050 fps for quiet suppressor work the only way you increase your energy/momentum on target is to increase bullet weight and eventually to do that you need bigger bores. I have a sub-sonic 450 Bushmaster load that is pushing nearly 1000 ft-lbs at the muzzle.

 

[gotboostvr]

I like straight wall cartridges for the deer hunting I do. Very thick flora and fauna, not enough range to nescietate a bottle necked cartridge anyways. Large calibres at moderate velocities don't destroy alot of meat either but do cause prolific wound channels and quick incapition.

 

[MTMilitiaman]

While I am not opposed to the idea, I feel like some here, that it is a bit of a niche caliber. It is bound to appeal almost exclusively to those hunting with an AR in states requiring straight-walled cartridges, and there is already a full market of established cartridges to fill this role. Those of us not bound by straight walled cases are still likely to prefer the original 6.8 SPC for hunting use.

 

[Varminterror]

The unfortunate reality we seem to be approaching is a situation where the wildcat juice simply won’t be worth the squeeze.

Incremental performance improvements over existing rounds - unless absolutely revolutionary and absolutely without fault - just don’t don’t seem to fly. We have the 6.5 PRC and 6 creed, both great improvements over the 6.5 creedmoor, but neither have enjoyed the meteoric rise. The 22 Nosler and 224 Valkyrie have proven greater performance over 223rem, but a few headaches in early launch and non-conventional parts have nearly stifled these rounds into the obscure corners of the gun world. The 45 GAP offered a size and weight advantage in a time focused on size and weight, but the advantage wasn’t enough to roll itself a spot in the market. RSAUM’s were a footnote behind the WSM’s, both of which were fantastic advancements over belted mags and long action standard cartridges, yet they all flicker in the edge of visibility rather than flourishing in the spotlight. None too invisible is all of the hate for the 6.5 creed’s popularity - even in light of its success - because of its small incremental improvements over previous cartridges. Nothing new exists under the sun, such launching competing products in this market is brutal at best.

I’d be certain in saying some folks have done straight/taper ~357-40cal Grendel/x39 and SPC cartridges as wildcats. Branch into bottlenecks and you see a never ending list of things which have been done - hell, Mike’s been doing his 358 WSM for a good long while too.

The heavy lift right now will be convincing broad market adoption for the .350 Legend. Diluting that effort with competing rounds in the same class, wavering consumer confidence with varying degrees of low level successes. What does seem to be real - rounds which use 5.56 mags and bolts are jumping on springs compared to non-standard bolt faces and cartridge bodies. I’d love to see multiple bolt faces as standard in the AR, but there’s really not a lot of room to do it. Proprietary bolts and mags with limited supply chain, and limited cartridge offerings are a challenge.

I keep 5.56, Grendel, and SPC uppers for breaking down and trying a few things here and there, and swapping bolts to get into something else isn’t so difficult. But having 10 different “standard” bolt faces in the AR platform doesn’t make sense.