Army chooses Sig Sauer to build Next Generation Squad Weapon.

[mav]

I was kinda kidding, lol.

But only kinda.

I figured, but it is a touchy subject around these parts

Nothing against AK's and all, just saying...

I'll also add that at least to me, it doesn't make a whole lot of sense given the ammo/supply constraint issues. The army is switching doctrine to focus on the Division as a self-supported fighting organization as opposed to the Brigade focus of the last 20+ years of "War on Terror" and urban pacification. There focus is on opposing peer Nation states going forward. All this discussion about lethality of round and defeating body armor is BS. The only peer nation that is fielding anything close is China. Russia is sending it's conscripts with 50+ year old body armor and China hasn't fought a war in 70 years and none of it's officers or nco's are combat proven. Why screw with something that works?

 

[Hailstorm]

The first problem would be finding a good American made AK

 

[Picton]

The first problem would be finding a good American made AK

That's why I wouldn't bother, honestly. Just use some old Romy stuff. Lol.

On this subject, I'm generally with the "if it ain't broke, don't fix it" crowd. I dislike the M16 "platform" for personal reasons, but it's shown itself to be an effective battle weapon. So why mess with it?

Innovation is important, and I get that it needs to be funded. But that's what DARPA or Natick are for. It doesn't need to be a splashy, large-scale shift, force-wide.

 

[juha_teuvonnen]

What's the point of the steel and brass case? Why not just make the whole case from steel or steel plated with some alloy? What am I missing?

As for the Army Times article, a couple of things seem odd:

1. Piston guns, when properly designed, are generally more reliable than direct impingement guns. Simply because the action is kept clean, by not sending gases back into it to cycle the weapon. If XM5 fails the mud test, it's not because of it being a piston gun, but because the design is piss poor. it can be redesigned. The AK and SKS have various flaws, but lack of reliability in dirty conditions isn't one of them.

2. I am unsure that you really need tungsten carbide to make AP rounds that go through Level 4 and 5 body armor. The Russians certainly don't think so. They just made the bullet cores from case-hardened tool steel (У12А). They made both 5.45x39 and 7.62x54R ammo with these cores. The former punches through 5mm armor plate at 250 meters, the latter sails through 10mm armor plate at greater distance.

 

[general disorder]

Wouldn't the whole thing be simpler if we just switched to a 77gr 5.56 round. Or if necessary a 308. Seems to be plenty of option already on the market without all this nonsense. but I also think it would've been easier if the military just switched to a Glock 17 instead of all this back and forth with the 320.

 

[Dench]

Wouldn't the whole thing be simpler if we just switched to a 77gr 5.56 round. Or if necessary a 308. Seems to be plenty of option already on the market without all this nonsense. but I also think it would've been easier if the military just switched to a Glock 17 instead of all this back and forth with the 320.

The Glock 17 thing was just another example of the army being retarded. They can't just accept what people make even though the vast majority of normal people around the world are fine with it. They have to have all these bozo requirements and then like we saw with the pistols ontop of that they go with the f***ing 320. Smart move, .mil. Go with the f***ing gun that just came out that may or may not have some problems over the 40 year old proven frame.

 

[SFC13557]

The Glock 17 thing was just another example of the army being retarded. They can't just accept what people make even though the vast majority of normal people around the world are fine with it. They have to have all these bozo requirements and then like we saw with the pistols ontop of that they go with the f***ing 320. Smart move, .mil. Go with the f***ing gun that just came out that may or may not have some problems over the 40 year old proven frame.

Yup.

 

[Fanucman]

What's the point of the steel and brass case? Why not just make the whole case from steel or steel plated with some alloy? What am I missing?

In order to push the heavier 6.8 round faster, they increased the chamber pressure from ~60,000 PSI to 80,000 PSI. They wanted a higher velocity because it is an easy way to pack more energy into each shot: Energy = Mass * Velocity^2
When they did that, the bases on the brass cases started failing, so they went to steel bases.
Originally they were a 4-piece design, but they simplified it and there is just a steel base and brass "tube" now.

I spoke to a Sig engineer in a class at Sig. He said they had the cost of making the 2-part "brass" down into the range of .308 brass now. Remember, making a brass case is pretty annoying. They start with a slug or disc of brass and have to press/spin it through many operations to form the brass case we know and love. Making it in 2 parts allows the manufacture of each half to be much more cheaply, but now the two halves need to be pressed (or welded, I am not sure) together.

I must admit I respect Sig for thinking "out of the box" and pushing the envelopes of what is possible in small arms, but that is where my enthusiasm for this concept ends...


In my poorly informed (and irrelevant) opinion, I think the Army trying to adopt the 6.8 round and a new rifle is idiotic.
Just look at the the American Rifleman magazine a couple months ago, where they had great data comparing rounds from armies around the world. The article is mostly about the squad automatic weapon version, but the info on the cartridges are still valid.
from An Official Journal Of The NRA | Return Of The Rifleman: The Next Generation Squad Weapons Program

The article is worth reading. By the numbers, the old .308 M-14 comes out looking darn good.
Sig's 6.8 looks worse than .308 in most categories and not significantly better than most rounds used by other armies today. It is heavier than the 5.56, so they have to reduce the number of rounds soldiers will carry. Sig's XM-5 rifles are also heavier than most other options and it seems to be expected that most will run with suppressors attached, making it more awkward (and light up like a beacon through thermals). I have not seen anyone talk about recoil, but if you are putting ~30% additional velocity into the bullet, that additional energy is obviously going right back into the shooter.
It does not seem like the extra energy per shot (bringing it up into the .308's energy) is worth adding an entirely new supply chain of ammo, magazines, rifles, parts, training, etc.

I suspect the Army is just bored with the M4/5.56, saw something new and shiny and grabbed it.

 

[juha_teuvonnen]

In order to push the heavier 6.8 round faster, they increased the chamber pressure from ~60,000 PSI to 80,000 PSI. They wanted a higher velocity because it is an easy way to pack more energy into each shot: Energy = Mass * Velocity^2
When they did that, the bases on the brass cases started failing, so they went to steel bases.
Originally they were a 4-piece design, but they simplified it and there is just a steel base and brass "tube" now.

I understand that it's the energy that kills, and that they went to steel because they needed stronger cases to cope with higher pressure. Why do they even need brass? What's wrong with all-steel cases? Steel cased ammo has been around forever and it works. Virtually all remotely modern Russian military ammo is steel cased. Steel is more abundant and cheaper than brass. May be there is something that I am missing, but I don't understand why brass part of the brass-and-steel case needs to be made from brass? What are the advantages over making the whole case entirely from steel? Russian cases are mild steel, may be mild steel wasn't strong enough to withstand 80K PSI? And cold-working better, stronger steel into a case was too expensive?

I understand the rationale behind the high velocity 6.8mm round. It's going to be more aerodynamic than anything .30 cal, IIRC the optimal diameter for projectiles in the 150 grain range is somewhere around the 6.5mm give o take a few tenths of a millimeter. The new round will have the velocity similar to that of the 5.56x45 out of a 14.5 in barrel. It will have a heavier bullet of 140 grains, almost like the 7.62x51. One thing I don't understand is the claim about low felt recoil. Unless the rifle has very effective recoil compensation devices, it has to kick similar or more than the 7.62x51. Newton's third and second law pretty much guarantee that. The acceleration has to be pretty brisk to make that 140 grain bullet leave the muzzle at 3000 fps. if you ask for my gut feeling, I'd expect recoil similar to .30-06 with 150-ish grain bullet.

Aerodynamics is important. 5.45x39 is a lower pressure round than 5.56x45, with lower muzzle velocity. It was done on purpose, to make weapon easier to control in full-auto. While 5.45 is initially slower than 5.56 it catches up somewhere around 300 years, due to better aerodynamics. I could see how a well designed 6.8mm bullet leaving the muzzle at 3000 fps could have better terminal ballistics throughout its effective range than a slower and less aerodynamic 7.62x51.

 

[Picton]

The Glock 17 thing was just another example of the army being retarded. They can't just accept what people make even though the vast majority of normal people around the world are fine with it. They have to have all these bozo requirements and then like we saw with the pistols ontop of that they go with the f***ing 320. Smart move, .mil. Go with the f***ing gun that just came out that may or may not have some problems over the 40 year old proven frame.

They really, really, REALLY like to believe off-the-shelf equipment, especially weapons, can't possibly be "good enough."

Mind-boggling, especially in the case of the Glock. I'm no Glock fan, but it's stupid to pretend it's not a well-designed weapons system with clockwork reliability, EASY maintenance, and a plethora of R&D already done and tested in many environments, with countless shooters using a million different accessories.

In other words, going Glock would make sense. Which is why the Army can't bring itself to do it.

 

[Parker Schreiber]

suspect the Army is just bored with the M4/5.56, saw something new and shiny and grabbed it.

A couple of counterpoints in fairness.

1. The figures in that chart seem to be based on the civilian hunting round, and even there the claimed muzzle energy is higher. The Milspec round should be beefier.

2. Of the three finalists, the Sig was considerably less shiny and gimmicky than either the Textron/H&K or General Dynamics/True Velocity candidates.

That doesn't mean that the procurement process wasn't badly broken, though.

 

[Fanucman]

... May be there is something that I am missing, but I don't understand why brass part of the brass-and-steel case needs to be made from brass? What are the advantages over making the whole case entirely from steel? ...

... One thing I don't understand is the claim about low felt recoil. Unless the rifle has very effective recoil compensation devices, it has to kick similar or more than the 7.62x51. Newton's third and second law pretty much guarantee that. The acceleration has to be pretty brisk to make that 140 grain bullet leave the muzzle at 3000 fps. if you ask for my gut feeling, I'd expect recoil similar to .30-06 with 150-ish grain bullet.

Lots of good questions. I don't know much more however.

The steel base of the 6.8 is stainless, and I presume stronger than Ruskie mild steel (not my area of expertise). I know Sig was proud that they were able to make the steel base thinner than the brass and that gave them a little extra space for more powder within the cartridge. Not sure why the entire thing is not stainless, maybe too difficult to work with? I thought I read something once about brass being better at carrying heat out of the gun, but I could be misremembering.

"Low felt recoil" could just be a reflection that Sig's rifle and SAW are heavier than their predecessors, especially with the suppressor attached. I don't think there is a muzzle device to help, the ones I have seen are simple and designed to host a silencer.

One of the reasons given for developing the XM5 and the new cartridge was that "the M16/5.56 has been pushed as far as it could go". To me, that is not necessarily a reason to change. They spent what, almost 60 years fixing the problems on the M16? So now it is time to throw it away?
Now that the AR is so popular in the civilian world, I suspect the rate of change is going to increase.

 

[paul73]

The steel base of the 6.8 is stainless, and I presume stronger than Ruskie mild steel (not my area of expertise). I know Sig was proud that they were able to make the steel base thinner than the brass and that gave them a little extra space for more powder within the cartridge. Not sure why the entire thing is not stainless, maybe too difficult to work with?

i can hardly understand the benefit of this, as those things are supposed to be made in billions. dunno. any complexity and costs in manufacturing of those cases is a minus, not a plus.

plus, anything that is getting connected at a seam will rip apart along that seam. it is just a must, it has to happen, if they connect base to the tube - the bases will be ripped out with brass tube left in the dirty barrel. i, kinda, guarantee that. (c) men`s warehouse

 

[general disorder]

In order to push the heavier 6.8 round faster, they increased the chamber pressure from ~60,000 PSI to 80,000 PSI. They wanted a higher velocity because it is an easy way to pack more energy into each shot: Energy = Mass * Velocity^2
When they did that, the bases on the brass cases started failing, so they went to steel bases.
Originally they were a 4-piece design, but they simplified it and there is just a steel base and brass "tube" now.

I spoke to a Sig engineer in a class at Sig. He said they had the cost of making the 2-part "brass" down into the range of .308 brass now. Remember, making a brass case is pretty annoying. They start with a slug or disc of brass and have to press/spin it through many operations to form the brass case we know and love. Making it in 2 parts allows the manufacture of each half to be much more cheaply, but now the two halves need to be pressed (or welded, I am not sure) together.

I must admit I respect Sig for thinking "out of the box" and pushing the envelopes of what is possible in small arms, but that is where my enthusiasm for this concept ends...


In my poorly informed (and irrelevant) opinion, I think the Army trying to adopt the 6.8 round and a new rifle is idiotic.
Just look at the the American Rifleman magazine a couple months ago, where they had great data comparing rounds from armies around the world. The article is mostly about the squad automatic weapon version, but the info on the cartridges are still valid.
from An Official Journal Of The NRA | Return Of The Rifleman: The Next Generation Squad Weapons Program

The article is worth reading. By the numbers, the old .308 M-14 comes out looking darn good.
Sig's 6.8 looks worse than .308 in most categories and not significantly better than most rounds used by other armies today. It is heavier than the 5.56, so they have to reduce the number of rounds soldiers will carry. Sig's XM-5 rifles are also heavier than most other options and it seems to be expected that most will run with suppressors attached, making it more awkward (and light up like a beacon through thermals). I have not seen anyone talk about recoil, but if you are putting ~30% additional velocity into the bSo

Solid info right there. And much appreciated. I just don't see much of an advantage that the 6.8 brings to the table over 7.62 nato. Is it better? Probably. Some. Maybe. but as it looks the juice isn't anywhere worth the squeeze.

 

[juha_teuvonnen]

Solid info right there. And much appreciated. I just don't see much of an advantage that the 6.8 brings to the table over 7.62 nato. Is it better? Probably. Some. Maybe. but as it looks the juice isn't anywhere worth the squeeze.

I could see how a modern, aerodynamic high velocity 6.8 would remain accurate and lethal three hundred yards further than 7.62x51. There are some engagement scenarios where that would be a significant advantage. If we were to adopt the russkie line of thought "infantry engagements in the field happen at 350 yards or less", then the extra range makes no difference.

 

[juha_teuvonnen]

Lots of good questions. I don't know much more however.

The steel base of the 6.8 is stainless, and I presume stronger than Ruskie mild steel (not my area of expertise). I know Sig was proud that they were able to make the steel base thinner than the brass and that gave them a little extra space for more powder within the cartridge. Not sure why the entire thing is not stainless, maybe too difficult to work with? I thought I read something once about brass being better at carrying heat out of the gun, but I could be misremembering.

Mild steel has low carbon content, so a garden variety mild steel will be more ductile and weaker than a garden variety Stainless. There are many different kinds of alloy steels, so a detailed discussion is pointless unless we know what kind of stainless Sig folks used. I know what steel the Russians used for their cases, and it's a very cheap, "nothing to write home about" kind. Because Stainless is less ductile and more brittle, cold-working it presents more of a challenge than mild steel. I suspect that it may be at least a part of the reason for the two-piece case design.

"Low felt recoil" could just be a reflection that Sig's rifle and SAW are heavier than their predecessors, especially with the suppressor attached. I don't think there is a muzzle device to help, the ones I have seen are simple and designed to host a silencer.

Well, a heavier weapon will obviously stay put. Technically that's cheating, because infantry loves lightening the load and for a good reason.

One of the reasons given for developing the XM5 and the new cartridge was that "the M16/5.56 has been pushed as far as it could go". To me, that is not necessarily a reason to change. They spent what, almost 60 years fixing the problems on the M16? So now it is time to throw it away?
Now that the AR is so popular in the civilian world, I suspect the rate of change is going to increase.

There are plenty of anecdotes from the recent Middle East wars where US servicemen would put 2-3 solid center mass hits into a local opponent weighting 130-160 lbs, we are not talking about a big guy. While the injuries were ultimately fatal for said opponents, often they were able to return fire before drawing their last breath. Unfortunately we lost some Soldiers and Marines this way. Terminal ballistics is an important consideration, and I see the value of a round that puts someone out of commission instantly, with proper shot placement.

 

[M1911]

My main concern is the extra weight. The last thing a grunt needs is a rifle system that adds another 3-5 lbs.

 

[40 Creedmoor fan]

They’ve tried caseless ammo to reduce weight, but I don’t think they’ve ever tried this increased pressure bi-metal setup before. R&D needs to happen. Without it, we’d still be using black powder and matchlock muskets.

I was thinking rifle designs when I wrote my comment but I see your point.

 

[40 Creedmoor fan]

One of the reasons given for developing the XM5 and the new cartridge was that "the M16/5.56 has been pushed as far as it could go". To me, that is not necessarily a reason to change. They spent what, almost 60 years fixing the problems on the M16? So now it is time to throw it away?

Now that the AR is so popular in the civilian world, I suspect the rate of change is going to increase.

There are plenty of anecdotes from the recent Middle East wars where US servicemen would put 2-3 solid center mass hits into a local opponent weighting 130-160 lbs, we are not talking about a big guy. While the injuries were ultimately fatal for said opponents, often they were able to return fire before drawing their last breath. Unfortunately we lost some Soldiers and Marines this way. Terminal ballistics is an important consideration, and I see the value of a round that puts someone out of commission instantly, with proper shot placement.

6.5 Grendel, 6 ARC, 300 Blackout. There cartridges can deal serious damage in an AR platform. None have been adopted. Shame.

 

[juha_teuvonnen]

6.5 Grendel, 6 ARC, 300 Blackout. There cartridges can deal serious damage in an AR platform. None have been adopted. Shame.

The designers of all of the above are calibers had to make some compromises to make them work with STANAG magazines and AR-15 type rifles. The army wasn't going to rebuild their existing rifles for the new caliber anyway, so they decided to ditch the AR-15/M-16/M-4 compatibility requirement. Which in turn opened the door to the use of heavier bullets and faster speeds than any of the above calibers.

 

[paul73]

I don’t think they’ve ever tried this increased pressure bi-metal setup before

i am really quite sure that it will become a tremendous shitshow for those bi-metal cases to rapture and leave its brass portion in the barrel.
it just got to happen, by any laws of logic and engineering, as anything connected is destined to disconnect, especially if it is a that sort of the juncture, steel to bronze.

 

[38ExtraSpecial]

The designers of all of the above are calibers had to make some compromises to make them work with STANAG magazines and AR-15 type rifles. The army wasn't going to rebuild their existing rifles for the new caliber anyway, so they decided to ditch the AR-15/M-16/M-4 compatibility requirement. Which in turn opened the door to the use of heavier bullets and faster speeds than any of the above calibers.

Arc is going about the same Speed as the 6.8. Also can be chambered in a standard ar15 platform.
Seem very much like the gov to want to abandon a platform for a supposed better one with better ammunition. Waste a ton of money and to find something that’s not better with a cartridge that doesn’t outperform the available offerings then scrap it and stick with old trusty. We’ve seen this a few times already.
6mm arc for the win.
Just as flat shooting as the 6.8. Less recoil. Lighter package. Platform already exists.

 

[PappyM3]

i am really quite sure that it will become a tremendous shitshow for those bi-metal cases to rapture and leave its brass portion in the barrel.
it just got to happen, by any laws of logic and engineering, as anything connected is destined to disconnect, especially if it is a that sort of the juncture, steel to bronze.

Perhaps. Unlike their civilian guns, Sig had done really extensive testing of the bi-metal cases for the NGSW program and it is apparently reliable. We’ll see if maybe prolonged sub-zero temperatures followed by firing cause them to separate?

Primers stay in place in military loads, so I’m not too inclined to believe a two piece case won’t as well.

 

[PappyM3]

Arc is going about the same Speed as the 6.8. …

How so?

135gr 6.8x51 from a 16” barrel: 3,000 fps
103gr 6 ARC from a 24” barrel: 2,800 fps

So, 6.8 gets you 32 grain more, going 200 fps faster, from an 8” shorter barrel. 6.8 will be about the same speed as 6 ARC, when shot from a 13” barrel. But it still has the grain and considerable short barrel advantages.

 

[paul73]

Perhaps. Unlike their civilian guns, Sig had done really extensive testing of the bi-metal cases for the NGSW program and it is apparently reliable. We’ll see if maybe prolonged sub-zero temperatures followed by firing cause them to separate?

Primers stay in place in military loads, so I’m not too inclined to believe a two piece case won’t as well.

life will tell. but the reloading aspect of that will probably not exist at all, as, not sure how many times this bi-metal weld will hold an 80k psi hit.

an interesting thing, though, as i think some folks were pushing old 308 into almost 90k psi with very hot loads. like a 50gr of h335. or imr4895.

 

[38ExtraSpecial]

How so?

135gr 6.8x51 from a 16” barrel: 3,000 fps
103gr 6 ARC from a 24” barrel: 2,800 fps

So, 6.8 gets you 32 grain more, going 200 fps faster, from an 8” shorter barrel. 6.8 will be about the same speed as 6 ARC, when shot from a 13” barrel. But it still has the grain and considerable short barrel advantages.

But you’re talking an AR10 sized cartridge. Comments above about lugging around an extra 2.5 pound of rifle.
I think SIG and the GOV just jumped too much.
We’re going from a 55 or 62 grain back up to a cartridge that’s basically what we tried to move away from for so many reasons. Why not meet in the middle at about double the weight of a 5.56 nominal load?

The ARC doesn’t lose much velocity in shorter barrels. It’s a very efficient cartridge and doesn’t need as much length to reach its potential. I’ve seen notes with almost 2700 FPS out of an 18”

Also it’s another cartridge that’s running low pressure 52k PSI. Bump that sucker up to a proper 60-65k PSI and what do you get? 3k FPS? Maybe I can run it through quick pads later tonight to see.

I’m a 308 guy. I also love the blackout. I think mass is awesome because it doesn’t diminish. Velocity does.
My opinion (you know what they say) is that the ARC or similar would have been an awesome cartridge and an easy change over for a proven platform.
If you wanted to stick to a .308 parent case the clear choice would be a 6.5 creedmoor or similar.
They over-engineered for very modest gains. That’s how cartridges and sometimes entire platforms die off.

 

[LakeTrout]

Arc is going about the same Speed as the 6.8. Also can be chambered in a standard ar15 platform.
Seem very much like the gov to want to abandon a platform for a supposed better one with better ammunition. Waste a ton of money and to find something that’s not better with a cartridge that doesn’t outperform the available offerings then scrap it and stick with old trusty. We’ve seen this a few times already.
6mm arc for the win.
Just as flat shooting as the 6.8. Less recoil. Lighter package. Platform already exists.

I wanted to love and build a 6 ARC. But the more I got into it the more I realized the numbers being touted on the internet were for a 24" bolt gun, and the 6 ARC in a carbine gas gun is nothing like those numbers. Doesn't shoot much flatter than a 6.5 grendel and doesn't hit as hard. I'm glad I didn't take the bait. The 6.8 is a totally different round and a far superior cartridge in every way out of a similar length gas gun.

 

[LakeTrout]

The ARC doesn’t lose much velocity in shorter barrels. It’s a very efficient cartridge and doesn’t need as much length to reach its potential. I’ve seen notes with almost 2700 FPS out of an 18”

Bolt gun? I've seen max loads out of a 22" gasser in the mid 2600s. Bolt guns can run higher pressure for this cartridge and a lot of the good velocity numbers on the internet reflect this and not gas guns. If you can point me to real data that an 18" gas gun is running SAAMI spec loads at around 2700 fps for the 108 grain bullets, which are the bullets that shoot the flattest and not the sub 100 grainers, I'll buy one tomorrow.

 

[PappyM3]

But you’re talking an AR10 sized cartridge. Comments above about lugging around an extra 2.5 pound of rifle.
I think SIG and the GOV just jumped too much.
We’re going from a 55 or 62 grain back up to a cartridge that’s basically what we tried to move away from for so many reasons. Why not meet in the middle at about double the weight of a 5.56 nominal load?

The ARC doesn’t lose much velocity in shorter barrels. It’s a very efficient cartridge and doesn’t need as much length to reach its potential. I’ve seen notes with almost 2700 FPS out of an 18”

Also it’s another cartridge that’s running low pressure 52k PSI. Bump that sucker up to a proper 60-65k PSI and what do you get? 3k FPS? Maybe I can run it through quick pads later tonight to see.

I’m a 308 guy. I also love the blackout. I think mass is awesome because it doesn’t diminish. Velocity does.
My opinion (you know what they say) is that the ARC or similar would have been an awesome cartridge and an easy change over for a proven platform.
If you wanted to stick to a .308 parent case the clear choice would be a 6.5 creedmoor or similar.
They over-engineered for very modest gains. That’s how cartridges and sometimes entire platforms die off.

It really doesn’t need to be an extra 2.5 lbs of rifle. The upcoming Steyr DMR rifle in 308/6.5 is supposed to be ~6.5 lbs. It’s not the cartridges fault that Sig made a porker.

And the development of the 6.8x51 gets you amazing performance in the great weighted M250. If we just stuck with implementing 6 ARC, we wouldn’t have gotten the new M250.

We also wouldn’t have gotten the high pressure, higher velocity bi-metal cases if we just abandoned R&D and implemented 6 ARC. The new case development went hand in hand with the rifle.

Though, I do think a bi-metal cased 80k psi 6 ARC with stronger bolt would be really interesting.

Speaking of bolts, that is a major consideration when thinking about 6 ARC or 6.5 Grendel for military use. The bolt is pretty thinned out for those cartridges. And regarding 300blk, that is a terrible cartridge for the objectives of the carbine modernization. Totally wrong ballistic profile.

I wonder if they just thought the juice for 6 ARC wasn’t worth the squeeze of a completely redone supply chain for a new caliber. That if they were going to do it, they’d want something with a bigger improvement.

If we’re looking for the easy button instead of investing in R&D, I do think a 6.5 CM 16” carbine would have been a great stop-gap to issue to a few soldiers per squad.

 

[38ExtraSpecial]

I wanted to love and build a 6 ARC. But the more I got into it the more I realized the numbers being touted on the internet were for a 24" bolt gun, and the 6 ARC in a carbine gas gun is nothing like those numbers. Doesn't shoot much flatter than a 6.5 grendel and doesn't hit as hard. I'm glad I didn't take the bait. The 6.8 is a totally different round and a far superior cartridge in every way out of a similar length gas gun.

Agreed but apples to oranges. The ARC and Grendel are similar but if you step up to the 6.8 size cartridge I would have picked the 6.5 creedmoor and I’m not a fanboy at all. I went .308 because I like it and there’s so much history and data and I’m classy type of guy unlike @Broc
I sure don’t see the benefit of 6.8 over 6.5

I also think there’s about 64 other cartridges in between that they could have picked.

Bolt gun? I've seen max loads out of a 22" gasser in the mid 2600s. Bolt guns can run higher pressure for this cartridge and a lot of the good velocity numbers on the internet reflect this and not gas guns. If you can point me to real data that an 18" gas gun is running SAAMI spec loads at around 2700 fps for the 108 grain bullets, which are the bullets that shoot the flattest and not the sub 100 grainers, I'll buy one tomorrow.

I can’t say definitively because I haven’t loaded or tested them myself.
I will try to get my friend to run some quick loads later for some real numbers. Well as close you real as you can get.