Let's design a new service rifle and cartridge...

[BrigandTwoFour]

A lot of discussion these days is focused on the current "big 3" alternate calibers of the AR-15 platform: 6.8 SPC II, 6.5 Grendel, and 300 BLK. Each one offers various gains (or losses) when compared to the standard 5.56 NATO round used in our beloved rifles. At the same time, in other areas, the gun world is abuzz with talk about how the Army effectively shut down the individual carbine competition.

This got me thinking. Why not start a discussion about what exactly a new rifle should look like? I don't want to limit it just to the rifle, though, so let's discuss the cartridge as well. All of the stuff that we've been talking about as far as cartridge variations and rifle design has been limited by two factors:

- All of the new carbine/rifle designs are based around continued use
of 5.56 and STANAG magazines

- All alternate cartridges we talk about have been a compromise of capability and the ability to fit into the AR-15 platform

So let's discard those requirements for this discussion. If you read the original ORO reports about the .223 and the AR-15, it becomes apparent that the story of the Ar-15 is every bit as much about the evolution of the .223. This discussion should be no different.

So here are the ground rules:

1. We must determine an ideal cartridge for general infantry issue. You cannot use theoretical technology that doesn't exist yet or will be difficult to obtain in quantity. Bullets must conform to current laws of armed conflict.

2. We must "design" a rifle to use said cartridge and be the standard issue long arm to US forces

3. Costs should be kept reasonable, but not stingy. This is all an academic exercise and does not need to fit into any actual fiscal policy. But the end result should still be practical.

Some considerations based on past experiences:

The original ORO research that led to the M-16 determined that an average military firefight (up through WWII) occurred within 100 yards. Beyond that range, hit probability decreased dramatically. Beyond 300 yards, the chance of being struck by a bullet was essentially random. Beyond 300 yards, you were about as likely to be killed by a grenade or artillery as you were a rifle round. The .223 was developed to meet this spec, though the maximum range spec was extended to satisfy the Marine Corps. While the historical engagement distance is relatively close, experiences in Afghanistan have demonstrated a need to have consistent capability at longer ranges.

During testing of the .223 and the M-16, penetration and intermediate barrier was found to be a significant issue when compared to the 7.62x51. Not much has changed in that regard; and the desire for a better performing round like the 6.8 SPC and 6.5 Grendel illustrate the fact. Whatever cartridge we come up with should demonstrate range, accuracy, penetration, and good terminal ballistics.

Accuracy through repeated fire was important during the original ORO tests. Whatever configuration we choose should continue in this tradition, but realize that the ammunition/weapon combination contracted today is 2 MOA to 6 MOA, not exactly precision work. Sacrificing precision in order to gain something else is acceptable, though the choice is up to you.

Useful References

Hitchman, N. (1952). Operational Requirements for an Infantry Hand Weapon.
http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=AD0000346

Ehrhart, T. (2009). Increasing Small Arms Lethality in Afghanistan:
Taking Back the Infantry Half-Kilometer.
http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf

[BrigandTwoFour]

To kick things off, here are my thoughts.

First, despite being active duty USAF, I honestly don't have any experience with using small arms in combat. My career field is nuclear weapons, not any direct action roles. And in seven years, the Air Force just hasn't seen fit to even let me qualify with anything other than the M9. But I am an unabashed technical nerd who reads and absorbs everything I can about small arms. I have played with a wide variety of arms, and have many friends who routinely go into harm's way in varying capacities including pilots, NSW, PJs, and other combat roles. We talk pretty often. That said, in my opinion, a new generation of infantry combat weapon would have a few basic characteristics:

1. As light as practical. With the trend towards heavier and heavier combat loads, the need for a lighter weapon grows more important. Research dating back to early last century also points out that being able to carry more ammunition dramatically increases the capability of the individual. We also have to consider the widespread entry of women into combat roles.

2. Modularity. I dislike quick swap barrels, as I think it introduces too many variables, but I do like the way an upper receiver can be swapped on the M4 or SCAR depending on the needed role. The ability for an individual to quickly tailor the weapon to their need is a force multiplier.

3. While I am a big fan of DI rifles, I think going to a piston system makes more sense for a hard use rifle. Improvements in the piston platform and manufacturing capability have mitigated the previously held concerns of accuracy and reciprocating mass on pistol rifles. I believe LMT and HK have demonstrated this with their piston platforms. That said, there is still a weight concern.

4. Any future combat rifle should be fully ambidextrous. Magazine release, bolt catch, and safety controls should all be readily available to the firing hand while maintaining a proper grip. I like a forward mounted non-reciprocating charging handle (a la the ACR).

5. I think an effective point target range of 500-700 meters is ideal for a general-purpose carbine/rifle. While the historical research showed the practical maximum range for most conflicts was 300 yards, recent experiences show that a longer capability is still needed.

As far as cartridges go, I really like the work that was done on the 6.8 SPC II. I think the .277 bullet provides a lot of opportunity, especially when more velocity can be gained. A 135 gr SMK launched at 2800 fps is still supersonic at 1000 yards, and still retains 800 ft-lbs of energy at 700 yards (enough to take down a deer). Additionally, the work done on the 6.8 SPC shows that shorter barrels can still provide plenty of velocity.

I think using the .277 bullet in a slightly larger case would provide the best balance of power, range, and capacity.

[TehLlama]

My first thoughts jumped to a slightly shorter iteration of the .276 Pedersen round - basically give that the treatment to where it runs like a slightly longer 6.8SPC in terms of chamber pressure and neck dimensions. Breaking from STANAG limitations, even if only a bit, may not happen, but it should for the purposes of this discussion.

I do like the polymer lower Aluminum upper setup used by the SCAR and Masada/ACR, and I'd agree that borrowing an existing piston system creates the greatest opportunity to field something useful. With those should be a simple ambidextrous pull down/push up bold release, otherwise both of those are good working examples.

Since multiple services are going to want a PDW variant, that needs to be considered in the design - but something like that with a 8"-12.5" barrel and collapsing/folding stock will fill the role adequately.

The biggest concern I have is that weight will be a compromise - for general infantry use, this will still come in at close to ten pounds when equipped with a Squad Common Optic, White/IR Light and Laser, Magazine, and Sling. This would be a great fighting gun out to 600m, for sure, but not be that handy in really urban fighting. Using a more PDW oriented version with a reflex optic could fix a lot of that, but this is back to the case where the entire family of weapons would need to be adopted before any logistics start to improve at all.

[Agnostic]

What about the 7 x 46mm uiac?

I know far too little to even attempt to put it into the ultimate service rifle.

[BrigandTwoFour]

Llama,

After you mentioned the PDW, I realized I had forgotten about the CZ Bren 805, which is another weapon that I think does a lot of stuff right. But, like the SCAR, the upper receiver just appears too "tall." I wonder if its even possible to keep a lower profile receiver while still using that style piston?

Agnostic,

I had never heard of that cartridge, and it looks really interesting. I didn't realize DocGKR had mentioned it in a thread here at M4C (https://www.m4carbine.net/showthread.php?t=19936). I wonder what the recoil comparison would be between the 7x46 and some higher powered varient of 6.8?

I come back to the training requirement. I feel like a lot of the reason we got away from the 7.62x51 as standard issue due to issues of weight and controllability in a standard rifleman platform under fully automatic fire. From a cost standpoint, it would take a lot more ammunition to properly train a single shooter with a heavier recoiling round.

The 7x46 does offer an interesting logistical aspect, though. If it can effectively replace both the 5.56 and the 7.62 for standard platforms, that helps the logistical supply chain quite a bit. Good find.

[Agnostic]

Llama,

After you mentioned the PDW, I realized I had forgotten about the CZ Bren 805, which is another weapon that I think does a lot of stuff right. But, like the SCAR, the upper receiver just appears too "tall." I wonder if its even possible to keep a lower profile receiver while still using that style piston?

Agnostic,

I had never heard of that cartridge, and it looks really interesting. I didn't realize DocGKR had mentioned it in a thread here at M4C (https://www.m4carbine.net/showthread.php?t=19936). I wonder what the recoil comparison would be between the 7x46 and some higher powered varient of 6.8?

I come back to the training requirement. I feel like a lot of the reason we got away from the 7.62x51 as standard issue due to issues of weight and controllability in a standard rifleman platform under fully automatic fire. From a cost standpoint, it would take a lot more ammunition to properly train a single shooter with a heavier recoiling round.

The 7x46 does offer an interesting logistical aspect, though. If it can effectively replace both the 5.56 and the 7.62 for standard platforms, that helps the logistical supply chain quite a bit. Good find.

That would be my question about it, weight and recoil.

[DocGKR]

A 6.5-7mm barrier blind projectile fired from a cartridge case with about 40 gr of capacity loaded with flash suppressed, heat stable powder optimized for full burn in a 16" barrel would be about perfect. Case head should be smaller diameter than current 7.62x51mm and case length should be a bit shorter--perhaps something around .440-460 base with a 46-47mm length; maybe using polymer case technology. Even better, something like a cased telescoping 7 mm could be used.

[Failure2Stop]

6.8 is hobbled from the start. The case wants and needs a larger receiver to do the job it is being asked to do. Are there benefits to the 6.8? Absolutely. But it would do even better if given the case capacity and structural support to push more.

Militaries and special units all over are coming back to 7.62, but not because they "need" 7.62, but rather that they need more than 5.56, and it is the simplest way to achieve the increase in effectiveness and range without going to specialty ammunition. If a true intermediate cartridge solution existed, I bet that it would gain a strong following. The issue is cost versus benefit, and frankly, the cost of retooling to build a new small arm cartridge is simply not worth the benefit in the grand scheme of things. This self imposed resistance to change stifles solutions.


Typos brought to you via Tapatalk and autocorrect.

[BoringGuy45]

6.8 is hobbled from the start. The case wants and needs a larger receiver to do the job it is being asked to do. Are there benefits to the 6.8? Absolutely. But it would do even better if given the case capacity and structural support to push more.

Militaries and special units all over are coming back to 7.62, but not because they "need" 7.62, but rather that they need more than 5.56, and it is the simplest way to achieve the increase in effectiveness and range without going to specialty ammunition. If a true intermediate cartridge solution existed, I bet that it would gain a strong following. The issue is cost versus benefit, and frankly, the cost of retooling to build a new small arm cartridge is simply not worth the benefit in the grand scheme of things. This self imposed resistance to change stifles solutions.


Typos brought to you via Tapatalk and autocorrect.

Exactly. I can't help wonder what the ballistics would be if the case were 45-47mm as opposed to 43.

[Failure2Stop]

I just want to clarify my previous post.

I am not saying that trying to advance is futile, simply that advancement on a "better than 5.56 cartridge" has been stifled due to budget constraints.