6mm Optimum in WW1

[sillygoose]

What if the militaries of Europe realize that a two caliber standard for infantry arms is the right way to go before WW1 and they work on developing an optimal infantry caliber for light weapons?

https://en.wikipedia.org/wiki/6mm_Optimum

Crist argued for the adoption of a 6mm rifle chambering as a replacement for the venerable 5.56×45mm NATO and 7.62×51mm NATO, calculating that such a loading would be near the weight and minimal recoil of the lightweight 5.56 while nearer the terminal performance of the heavier 7.62, thereby permitting a single caliber to serve in general-purpose machine guns, sniper rifles, and infantry carbines.[1][2]

Crist's specifications were that "6mm Optimum" ammunition achieve, with a 100 gr (6.5 g) bullet:

• Muzzle velocity: 880 m/s (2,900 ft/s)
• Velocity at 1200 m: 350 m/s (1,149 ft/s) (slightly over the speed of sound)
• Muzzle energy: 2,531 J (1,867 ft⋅lbf)
• Energy at 1200 m: 397 J (293 ft⋅lbf)
• Flight-time to 1200 m: 2.21 seconds
• Deflection at 1200 m: 3.8 m (151 in) in 4.5 m/s (10 mph) wind speed
• Maximum trajectory height: 6.2 m (244 in)

...of which he noted, "...even with a conservative estimate for the muzzle velocity of the 6mm Optimum cartridge, computed data for 1200-meter velocity, flight-time, wind-deflection, and trajectory height are all greatly superior to both 5.56 and 7.62 NATO rounds."[1]

The French developed something like this in the early 1900s:

Meunier rifle - Wikipedia

en.wikipedia.org

Cartridge development[edit]
The Section Technique de l'Artillerie (STA) developed various rimless high performance cartridges from 1890 to 1912. Among these cartridges, some were retained:

• 6×58 Meunier 1897
• 6×60 ENT, 1900
• 6.5×60 CAP 1905
• 6.5×61 STA 1910
• 6.5×55.5 Berthier 1910
• 7×59 STA 1912
• 7×57 Meunier 1912

Theirs were very hot though and would have been barrel burners, hence the final toned down 7x57mm cartridge for the Munier rifle. But what if they realized the 6mm caliber was the way to go for most infantry roles and they settled on that while making their 8mm cartridge into an HMG caliber? Let's say they do that in 1903-5 when that was the favored caliber.

The rest of Europe could follow quickly, as the British also ended up developing a 7mm Enfield cartridge, but delayed like the French so that it never saw use in WW1 in any significant capacity.

The virtues is a cartridge that could still reach out to 1000m, use a shortened existing cartridge case for most countries (provided also made rimless), be quite light recoil, and would allow for nearly double the ammo per same amount of weight. Plus less material means more savings in general to make.

Leaving the larger calibers for HMG units wouldn't be a significant problem logistically given how HMGs were treated in 1914 as effectively artillery pieces and that could also allow for them to be made more powerful for longer range and AP work, much like how the Swedes used 6.5mm general purpose cartridges, but a powerful 8mm one for HMGs:

https://en.wikipedia.org/wiki/8%C3%9763mm_patron_m/32

Also the lighter cartridge means rifles/carbines and LMGs/auto-rifles could be made lighter as well as one day evolve into SLR/battle rifle cartridges with little to no modification.

How might this POD impact the battlefield in WW1? Recoil would be close to half that of the OTL cartridges, about twice as many rounds could be carried, heat buildup would be about half as well, accuracy would be higher, barrels could be shorter, less materials could be used, and SLRs would be much easier to make (same with LMGs/auto-rifles) not to mention cheaper. Also keep in mind until 1916 bullets inflicted more casualties than artillery in WW1.

Might weapons like the Lewis Gun and Chauchat (or Madsen) have been lighter and more reliable/useful with a cartridge like this? The Chauchat had a problem of overheating with the 8mm Lebel and even worse one with the .30-06. The Lewis gun had that expensive and overly complicated forced induction barrel shroud. Or would even a light belt-fed MG be viable with a fixed barrel like the RPD? Certainly the French had some interesting 6mm designs pre-war for an auto-rifle, effectively a pre-war BAR in 6mm:

https://en.wikipedia.org/wiki/Rossignol_ENT

 

[Buba]

Yes, something like the 6,5x50 Arisaka or the 6,5x52/54 Carcano/Mannlicher would had been better than OTL. Better, but not a game changer.
The 7,62x39 - in 6,5mm - would had been best, naturally
Would "heat build up" be an issue for turnbolt repeater rifles? Or are you thinking about LMGs?
1000m is too much - who cares about individual rifleman accuracy over 400m? Freaks!
But the cartridge is only part of the "system" - PBI might still end up saddled with rifles sporting a "manly" 75cm long barrel ...
The main issue is mentality - belt fed (metallic belt!) GPMG were available in 1915/6 (Bergmann MG 15) - and so what? The Darne company was offering a family consisting of automatic rifle, magazine fed LMG and belt fed M/HMGs from 1923 onward - but so what? Nobody adopted the concept until almost 15-20 years later - the MG34.

Some interesting reading (I hope):

https://www.quarryhs.co.uk/Historic%20MGs.htm

 

[sillygoose]

Yes, something like the 6,5x50 Arisaka or the 6,5x52/54 Carcano/Mannlicher would had been better than OTL. Better, but not a game changer.
The 7,62x39 - in 6,5mm - would had been best, naturally

You mean the 6.5 Grendel. The 6mm Optimum is basically a 6mm Grendel.
Hence why I did this thread....it is the best

https://en.wikipedia.org/wiki/6.5mm_Grendel

The case head diameter of the Grendel is the same as that of the .220 Russian, 7.62×39mm and 6.5mm PPC cases.

https://en.wikipedia.org/wiki/6mm_AR

The cartridge uses a 6.5 Grendel case that has been necked-down to accept a 6.2 mm (.243 in) bullet.

https://en.wikipedia.org/wiki/6mm_Optimum

If you check the links the performance is just under the 6mm Optimum, but so close that it really doesn't matter.

Would "heat build up" be an issue for turnbolt repeater rifles? Or are you thinking about LMGs?
1000m is too much - who cares about individual rifleman accuracy over 400m? Freaks!
But the cartridge is only part of the "system" - PBI might still end up saddled with rifles sporting a "manly" 75cm long barrel ...
The main issue is mentality - belt fed (metallic belt!) GPMG were available in 1915/6 (Bergmann MG 15) - and so what? The Darne company was offering a family consisting of automatic rifle, magazine fed LMG and belt fed M/HMGs from 1923 onward - but so what? Nobody adopted the concept until almost 15-20 years later - the MG34.

Heat build up I am thinking about both. Bolt actions get real hot with WW1/2 cartridges after less than 10 rounds.

1000m is too much, but I'm thinking of how to get this done given the bias towards the 'kill a horse at 1000m' philosophy of the time.

To get the performance needed a carbine (by WW1 standards) length barrel would do, so 60cm (or 24 inches for us Americans).

The Bergman in 6mm optimum though even an air-cooled version could have been viable and much less heavy, while the air cooled feature would have been sufficient. In fact it was basically a MG34 minus the QC barrel. Given the lower heat build up a low ROF version around 400 RPM would have been fantastic for the era and have provided light mobile firepower.

Similarly a British version in the Lewis Gun would have been excellent as well even with the barrel shroud. The Chauchat might have even been viable, but the Rossignol ENT would probably have been adopted instead...which would have been like the BAR and an excellent weapon. So much so that having it in 1914 in quantity might have even seriously limited the German advance and jacked up losses to an unsustainable degree.

Some interesting reading (I hope):

https://www.quarryhs.co.uk/Historic%20MGs.htm

I've read that one before. The Lee Navy is the criminal disregarded round of the 20th century.

 

[bintananth]

You mean the 6.5 Grendel. The 6mm Optimum is basically a 6mm Grendel.
Hence why I did this thread....it is the best

https://en.wikipedia.org/wiki/6.5mm_Grendel

https://en.wikipedia.org/wiki/6mm_AR

https://en.wikipedia.org/wiki/6mm_Optimum

If you check the links the performance is just under the 6mm Optimum, but so close that it really doesn't matter.


Heat build up I am thinking about both. Bolt actions get real hot with WW1/2 cartridges after less than 10 rounds.

1000m is too much, but I'm thinking of how to get this done given the bias towards the 'kill a horse at 1000m' philosophy of the time.

To get the performance needed a carbine (by WW1 standards) length barrel would do, so 60cm (or 24 inches for us Americans).

The Bergman in 6mm optimum though even an air-cooled version could have been viable and much less heavy, while the air cooled feature would have been sufficient. In fact it was basically a MG34 minus the QC barrel. Given the lower heat build up a low ROF version around 400 RPM would have been fantastic for the era and have provided light mobile firepower.

Similarly a British version in the Lewis Gun would have been excellent as well even with the barrel shroud. The Chauchat might have even been viable, but the Rossignol ENT would probably have been adopted instead...which would have been like the BAR and an excellent weapon. So much so that having it in 1914 in quantity might have even seriously limited the German advance and jacked up losses to an unsustainable degree.


I've read that one before. The Lee Navy is the criminal disregarded round of the 20th century.

Umm ...

I use 0.58" ball when I'm out hunting. That's 14.7mm and just shy of a crew-served cannon round.

 

[sillygoose]

Umm ...

I use 0.58" ball when I'm out hunting. That's 14.7mm and just shy of a crew-served cannon round.

Next time try a 155mm howitzer.

 

[bintananth]

Next time try a 155mm howitzer.

No thanks.

I know what the Fire Marshall will say when crew-served artillery is fired indoors. I'll stick to things that aren't crew-served, TYVM.

 

[ATP]

Yes, something like the 6,5x50 Arisaka or the 6,5x52/54 Carcano/Mannlicher would had been better than OTL. Better, but not a game changer.
The 7,62x39 - in 6,5mm - would had been best, naturally
Would "heat build up" be an issue for turnbolt repeater rifles? Or are you thinking about LMGs?
1000m is too much - who cares about individual rifleman accuracy over 400m? Freaks!
But the cartridge is only part of the "system" - PBI might still end up saddled with rifles sporting a "manly" 75cm long barrel ...
The main issue is mentality - belt fed (metallic belt!) GPMG were available in 1915/6 (Bergmann MG 15) - and so what? The Darne company was offering a family consisting of automatic rifle, magazine fed LMG and belt fed M/HMGs from 1923 onward - but so what? Nobody adopted the concept until almost 15-20 years later - the MG34.

Some interesting reading (I hope):

https://www.quarryhs.co.uk/Historic%20MGs.htm

Russians made first assault rifle,Avtamat fedorova,for Arisaka ammo.The same could be done to 6mm.
Good idea,i think.

 

[sillygoose]

Russians made first assault rifle,Avtamat fedorova,for Arisaka ammo.The same could be done to 6mm.
Good idea,i think.

Seems it was more of an auto-rifle than an assault rifle in terms of its role, like the BAR. Fedorov wanted to make a much higher powered 6.5mm cartridge like the 6.5 Swedish, but during the war they couldn't make new ammo, so had to buy a bunch of 6.5mm from Japan. Due to the lower power it allowed the rifle to be made much lighter and be more controllable than Fedorov intended originally. Interestingly if you check out Fedorov's notes he was a quite smart guy who calculated that 6mm was the most desirable caliber due to weight and sectional density, but didn't want to risk using the caliber since there was no significant examples used by any military in the world, so settled on 6.5mm instead.

Anyway in 6mm it looks like the French had a working automatic rifle design in 6mm as early as 1903, but didn't decide on using that caliber, so scrapped the design; it was supposed to have been the basis for a 6mm SLR and autorifle:

https://en.wikipedia.org/wiki/Rossignol_ENT

If the French had both the SLR and autorifle in 1914 in large numbers they could have made the Germans' lives very tough and probably short. They'd have had to tone down the ammo's power to make it viable IMHO, but having a BAR equivalent in 6mm, one per squad, in 1914 plus a bunch of semi-autorifles in the same caliber would have drastically increased firepower. I'm thinking probably 300% over the standard bolt action equipped squad of 1914 without an automatic weapon. Good luck advancing in an open field against that with just bolt actions for suppressive fire. Unless you have crushing superiority in numbers and HMGs as well as artillery.

If they could get two per squad it would be even better.

The Bergman 15 na belt fed would have been an excellent counter especially if made even lighter due to the lower powered cartridge.

 

[Buba]

As to the Bergmann MG15 - I was thinking about it (once modified to air cooled)) as a GPMG weapon issued at company level - with bipod, or higher - with tripod, and using whatever 7-8mm full power rifle cartridge that particular army was using (or hotter, e.g. German 9x62mm or 8x64mm by Brenneke). Or something like that - and fully possible by 1900 - the Hotchkiss comes to mind as first.
I was not thinking about it as a magazine fed LMG chambered in wonder 6mm and issued at squad level.
With a real LMG - unlike the wannabe BAR- there is no need to issue two per squad.

 

[sillygoose]

As to the Bergmann MG15 - I was thinking about it (once modified to air cooled)) as a GPMG weapon issued at company level - with bipod, or higher - with tripod, and using whatever 7-8mm full power rifle cartridge that particular army was using (or hotter, e.g. German 9x62mm or 8x64mm by Brenneke). Or something like that - and fully possible by 1900 - the Hotchkiss comes to mind as first.

The problem with the Bergman in standard caliber is the fixed air cooled barrel which limits it to one belt until it cools down. So if you had 4-6 or so per company concentrated you'd have to stagger their firing with one firing at a time and switching off as the spent time cooling down for a few minutes between belts.

Using the higher powered 8mm or 9mm would require using the MG08 or Maxim/Hotchkiss/Vickers with water cooling.

The French did after WW1 settle on a 9x66mm MAS HMG as they determined the 8mm wasn't enough, but the 13mm was overkill. They only had prototypes ready by 1940. Basically it was the original LWMMG in .330 caliber.

I was not thinking about it as a magazine fed LMG chambered in wonder 6mm and issued at squad level.
With a real LMG - unlike the wannabe BAR- there is no need to issue two per squad.

At the platoon level it would be viable in 6mm. The lower heat build up would let it go through two belts before cooling down. So having 2-3 at the platoon level would allow them to alternate firing and have reduced cooling cycles if they stuck to firing off one 250 round belt at a time and having say a 400-500 rpm rate. 30-60 second cooling cycle should be fine then.

Belt feds at the squad level are problematic, which is why the Brits, US, USSR, and French went with the magazine fed LMGs/autorifles in WW2. Even the Germans by the end kicked their LMGs up to the platoon and were trying to go with assault rifles only at squad level.

 

[Buba]

Sorry for lack of clarity - I envision two different weapons. One chambered in 8-9mm at coy/bat level, belt fed, and another - in Wonder Six - magazine fed, at squad level. The bigger weapon could use some sort of recoil operation (like the Bergmann), while the SAW would be gas operated (Hotchkiss, Lewis, etc.).

BTW - the platoon/coy level belt fed weapon would use 50 (max 100) round belts in drums (again - Bergmann in WWI) attached to weapon for mobility, while at higher levels 200-250 belts would be in boxes standing alongside the tripod.

the Germans by the end kicked their LMGs up to the platoon and were trying to go with assault rifles only at squad level.

IMO indeed a case can be made that the assault rifle killed off the need for squad level LMG. But WWI is too early for that

 

[sillygoose]

Sorry for lack of clarity - I envision two different weapons. One chambered in 8-9mm at coy/bat level, belt fed, and another - in Wonder Six - magazine fed, at squad level. The bigger weapon could use some sort of recoil operation (like the Bergmann), while the SAW would be gas operated (Hotchkiss, Lewis, etc.).

From what I can find from WW1 at all stages of the war proper MGs were battalion weapons due to their weight. So the mag fed automatics would be a squad/platoon weapon. In the German case, since we are talking about the Bergmans, they'd keep the MG08 at the battalion level where the weight would be a non-issue. A mag-fed Bergman though could be at the squad or platoon level. No reason to make a gas operated MG as the Bergman was short recoil and performed well, as did the later MG34/42 at squad level.

BTW - the platoon/coy level belt fed weapon would use 50 (max 100) round belts in drums (again - Bergmann in WWI) attached to weapon for mobility, while at higher levels 200-250 belts would be in boxes standing alongside the tripod.

Seems like the preference in all armies was to have a squad automatic and a battalion MG unit, but no platoon or company MGs or automatics. Info is somewhat scarce online, but that is the way the US and UK did it from what I could find and IIRC the Germans did too. No info about the Russians or Italians. The French had 1-2 Chauchat IOTL by 1917, but here might start with the Rossignol or later adopt the Chauchat in 6mm.

IMO indeed a case can be made that the assault rifle killed off the need for squad level LMG. But WWI is too early for that

Agreed, unless some big brain pulls off the delayed blowback operating system...

https://en.wikipedia.org/wiki/Ferdinand_Mannlicher#Mannlicher's_automatic_rifle_designs

The model 93 semi-auto delayed blowback rifle in 6mm 'short' could work. I'd think for the design they'd have to adapt the 8x57mm cartridge down to a 6x40/42mm version, but that should help reduce the violent ejection somewhat and make the overall design lighter with less recoil. Then there was his Model 83 semi-auto or 85 automatic rifle, both using a short recoil operating system like the Bergman or later Johnson rifle.

If the Austro-Hungarians had gotten funding they could have had an excellent series of small arms going into WW1 to make up for their lack of trained manpower and would well supplement their offensive doctrine. NGL I've got a soft-spot for the Austrians in WW1, so it would be highly interesting to think of their forces going to battle in 1914 with 6mm semi-auto magazine fed delayed blowback rifles and short-recoil automatic rifles at the squad level, and belt fed 8mm Schwarzlose MGs at battalion level.

The toggle delayed blowback operating system could have been developed for use in the automatic rifle too if desired.

Such a combo would be pretty deadly against the Russians in the open fields of Galicia in 1914, which was primarily an infantry fight outside of East Galicia in August. Certainly would help against the Serbs too.

 

[Buba]

Seems like the preference in all armies was to have a squad automatic and a battalion MG unit, but no platoon or company MGs or automatics.

The British issued 36 (2 per platoon +4 spare) LMGs at Battalion level. These were then shared around. At least at some point ...

Not sure at what level the 08/15 was issued.
The final form was aircooled, the 08/18 - too late for combat. The entry for this weapon on the Polish Armed Forces Musem page is rather critical of it.

Muzeum Wojska Polskiego w Warszawie

EMWPaedia to autorski projekt pracowników Muzeum Wojska Polskiego w Warszawie, w którym umieszczane będą hasła dotyczące militariów i rygorystycznie traktowanej historii oręża i wojskowości.

www.muzeumwp.pl

 

[sillygoose]

The British issued 36 (2 per platoon +4 spare) LMGs at Battalion level. These were then shared around. At least at some point ...

Sounds about right from what I could find. They divided the Platoons into sections with specialist jobs. The automatic section concentrated the LMGs in one squad it seems.

Not sure at what level the 08/15 was issued.
The final form was aircooled, the 08/18 - too late for combat. The entry for this weapon on the Polish Armed Forces Musem page is rather critical of it.

Muzeum Wojska Polskiego w Warszawie

EMWPaedia to autorski projekt pracowników Muzeum Wojska Polskiego w Warszawie, w którym umieszczane będą hasła dotyczące militariów i rygorystycznie traktowanej historii oręża i wojskowości.

www.muzeumwp.pl

Squad as well. But it was heavy AF.
Sounds like the MG08/18 was just the Bergman 15 na but heavier.