US adopts 6mm caliber in 1930s

[Deleted member 1487]

So I came across a very interesting historical report a little while back:
https://www.everydaymarksman.co/resources/kent-report-1930/

Basically a guy at the Aberdeen Proving Grounds was advocating for a small caliber, high velocity cartridge in 1930(!) and wrote a technical report about why the concept was superior to the existing .30 caliber and was later republished when the push for the 5.56mm cartridge came in the late 1950s:
https://apps.dtic.mil/dtic/tr/fulltext/u2/705381.pdf

Part of the reason it wasn't due to the 1000m standard of the day. Thing is the 6mm caliber is capable of being a 1000m round, as has been shown by the marksmen community today (6mm caliber is one of the most popular for long range shooting) and by work done in the 1970s on the 6mm SAW cartridge and as argued in the 1990s by Stanley Crist:
https://www.g2mil.com/6mm_optimum_cartridge.htm

So what if some enterprising officer like Julian Hatcher took note of the report and resurrected the 6mm Lee Navy with a modern spitzer boat tail design and got it accepted as the basis for the US Army semi-automatic rifle project? The .30-06 would remain the belt fed machine gun caliber, but all the other rifles and autorifles would use the modernized '6mm Hatcher Army' cartridge. This would retire the BAR, as it was way too much gun for the cartridge, and open things up to a lighter Johnson LMG and larger capacity Garand.

That not only makes the Garand considerably lighter and arguably easier to design given the light recoil of the round, but also does the same for an automatic rifle while enabling at least a 30 round magazine. Meanwhile the ballistics and penetration ability of the bullet would be substantially better than the .30-06 M2 Ball due to the ballistic form and sectional density of a long 6mm bullet, which also grants it a better ability to tumble if the ogive of the nose is long enough (helps shift the center of gravity to the rear) and that was the effect of the 6mm Lee Navy back in the 1890s.

Seems like it would grant a pretty decisive small arms advantage, especially as it would allow an autorifle/LMG to be less than 5kg and arguably cheap enough to make 2-3 per squad viable compared to the BAR, which only had production large enough in 1944 to really allow for that, but still weighed nearly 9kg, double the weight of something like a 6mm Johnson LMG (the .30-06 version was less than 6kg). Not only that, but the ammo would be about half as heavy if the 6mm Lee Navy cartridge is anything to go by (this round would be lighter), which enhances the firepower of a unit equipped with it, as they could fire a lot more lead at the enemy than with the .30-06. It would also heat up less quickly due to the lower powder charge too.

So thoughts? Seems like the US Army could have it's cake (1000m range) and eat it too (all the benefits of small caliber while still having a role for the .30-06 stockpiles without having to design a new bullet for the Garand).

 

[Oldbill]

This is a nice idea. The lessened recoil in going from 30.06 to 6mm is significant, meaning an easier time to stay on target or get the next shot off.

 

[James Ricker]

For the most part World War II was an infantry slugging match. Higher power for American forces would mean higher attrition for the axis forces. The Americans when take the islands in the Pacific a little faster with fewer casualties. The driving to Germany would go a little faster and the Germans would start running out of manpower a little earlier. The war in Europe would be shortened buy a month of most. The timeline of the war in the Pacific would not be altered.

 

[Peg Leg Pom]

The US (Navy) adopted (briefly) the 6mm Lee Navy in 1895.

 

[MichaelWest]

My suspicion is that the culture of the day is not ready for such a modern approach. The Garand was quite a step forward from the bolt action, the BAR shows how lagging was small unit supporting fire thought was compared to the GPMG we know as the MG34. The average Colonel and General with WW1 experience was still thinking heavy bullet, accurate fire, some greater volume but not so much as to outstrip the load per man. But could we see it filter over to the Carbine? The M1 Carbine was almost what you described but its round not quite potent enough. That might give us a full auto capable assault style rifle to employ in compliment to the M1/BAR pair, paving the way to a better follow on yo M1 than M14?

 

[Deleted member 1487]

My suspicion is that the culture of the day is not ready for such a modern approach. The Garand was quite a step forward from the bolt action, the BAR shows how lagging was small unit supporting fire thought was compared to the GPMG we know as the MG34. The average Colonel and General with WW1 experience was still thinking heavy bullet, accurate fire, some greater volume but not so much as to outstrip the load per man. But could we see it filter over to the Carbine? The M1 Carbine was almost what you described but its round not quite potent enough. That might give us a full auto capable assault style rifle to employ in compliment to the M1/BAR pair, paving the way to a better follow on yo M1 than M14?

Certainly it could work for the M1 Carbine too, though with the light 6mm cartridge for the Garand it might be viable to make that into a carbine version like they attempted for the historical Garand.

 

[Deleted member 1487]

For the most part World War II was an infantry slugging match. Higher power for American forces would mean higher attrition for the axis forces. The Americans when take the islands in the Pacific a little faster with fewer casualties. The driving to Germany would go a little faster and the Germans would start running out of manpower a little earlier. The war in Europe would be shortened buy a month of most. The timeline of the war in the Pacific would not be altered.

So Wallies take Berlin and all the people that died in the last 30 days of the war due to Nazi atrocities are spared?

 

[MichaelWest]

Certainly it could work for the M1 Carbine too, though with the light 6mm cartridge for the Garand it might be viable to make that into a carbine version like they attempted for the historical Garand.

My thinking would be your 6mm Garand eliminates the M1 Carbine, it should be light enough to flex into the role, otherwise maybe the SMG is issued to rear area troops?

 

[Deleted member 1487]

My thinking would be your 6mm Garand eliminates the M1 Carbine, it should be light enough to flex into the role, otherwise maybe the SMG is issued to rear area troops?

Perhaps? The 6mm cartridge would be pretty powerful for a rifle as light as the M1 Carbine was, which it likely won't be able to approach in weight, even with a muzzle brake. The only SMG around early in US participation in WW2 was the Thompson SMG which was heavier than the Garand. Though in the name of production/logistics ease they might just make a lightened carbine version of TTL's 6mm Garand and say 'good enough'. After all the Euros issued bolt actions to their rear area personnel and got along fine. Even their SMGs were heavier than the M1 Carbine, so in lieu of an M3 Grease Gun at the time the US military might just do a carbine-d Garand, especially if the shortened barrel, folding stock 'tanker' Garand is viable. I'd imagine the Grease Gun shows up on time ITTL, just no M1 Carbine or BAR.

That would make things interesting post-WW2 vis-a-vis the NATO cartridge, as it is likely NATO just opts to adopt the 6mm cartridge and .30-06. If the Johnson LMG works out that might soldier on for a while, but perhaps the US does make an M60 in both 6mm and .30-06 in time for Vietnam.

As a counterpoint the report does mention that a .20 caliber round would be ideal out to 500 yards due to it's flat trajectory and low recoil and potential to be very lethal at high speeds, so perhaps OTL .30 Carbine becomes TTL's .20 Carbine. It would be somewhat similar to the .204 Ruger (which has an insane 250m zero!), though considerably less powerful and therefore lighter and much lower recoiling. A M1 Carbine then could be even lighter than IOTL and fully controllable in automatic, plus a 30 round magazine would be pretty necessary in that case. A folding stock version would entirely replace the SMG as a weapon and be vastly cheaper than the Thompson and potential cheaper than even the Grease Gun if it eliminates the .45 caliber entirely and with it the M1911. As it was the paratrooper M1 Carbine with folding stock had a holster like a large pistol:

In that case goodbye tanker Garand.

 

[JSchafer]

6.5 would be a better fit. 6 and under are heavily impacted by strong winds.

 

[Deleted member 1487]

6.5 would be a better fit. 6 and under are heavily impacted by strong winds.

Apparently not a significant amount at 1000m:
https://www.eagleeyeammo.com/blog/6mm-creedmoor-vs-65-creedmoor-a-ballistic-comparison/

 

[SsgtC]

The biggest problem to getting a new caliber adopted is the several million rounds of .30-06 in inventory. You need to find a way around that issue before the Army will ever actually switch calibers. The only way I can see that happening is the new round has to have significantly increased performance over the .30-06. And it has to be so superior that the Army can't deny it or hide behind bull crap requirements like "stopping a charging horse"

 

[Deleted member 1487]

The biggest problem to getting a new caliber adopted is the several million rounds of .30-06 in inventory. You need to find a way around that issue before the Army will ever actually switch calibers. The only way I can see that happening is the new round has to have significantly increased performance over the .30-06. And it has to be so superior that the Army can't deny it or hide behind bull crap requirements like "stopping a charging horse"

The US military today recognized that significant improvement and is shifting to 6.5mm and 6.8mm:
https://uklandpower.com/2018/10/31/...usasoc-6-5-mm-precision-intermediate-calibre/
https://www.popularmechanics.com/mi...-round-special-ops-getting-new-sniper-bullet/
https://www.militarytimes.com/news/...cs-will-make-soldiers-marines-a-lot-deadlier/

The .30-06 caliber would still be used ITTL, just for medium and heavy MGs.

 

[Dave Shoup]

This is a nice idea. The lessened recoil in going from 30.06 to 6mm is significant, meaning an easier time to stay on target or get the next shot off.

It's an interesting idea, but US Army Ordnance had - arguably - a similarly "lighter" cartridge in hand in the .276/7mm in the 1920s, designed for the proto-Garand, and its adoption foundered on the simple reality the US had millions of rounds of 30.06 in storage, as well as hundreds of thousands of rifles and machine guns that fired the same cartridge, in service and in storage.

 

[marathag]

and its adoption foundered on the simple reality the US had millions of rounds of 30.06 in storage, as well as hundreds of thousands of rifles and machine guns that fired the same cartridge, in service and in storage.

I've never came across a thing on the BAR or MGs going to the new caliber.
And once more, I'll beat that old drum--
Not a single Round of that warehoused 30-06 made it into Garand chambers during WWII

 

[Dave Shoup]

I've never came across a thing on the BAR or MGs going to the new caliber.
And once more, I'll beat that old drum--Not a single Round of that warehoused 30-06 made it into Garand chambers during WWII

Perhaps, but that's hindsight. To the general officers - like MacArthur - who had seen the mobilizations in 1898 and 1917-18 up close and personally, to expect that a US Army facing a Pacific War in the 1920s or 1930s was not going to use every round in storage and then some is asking a lot.

 

[SsgtC]

I've never came across a thing on the BAR or MGs going to the new caliber.
And once more, I'll beat that old drum--
Not a single Round of that warehoused 30-06 made it into Garand chambers during WWII

Be that as it may, that won't change the Army decision makers minds in the relevant time period. And the main reason given for not switching calibers, was the sheer amount of ammunition in storage in the .30-06 caliber. That will still be a primary consideration when evaluating a new caliber.

 

[MichaelWest]

Perhaps? The 6mm cartridge would be pretty powerful for a rifle as light as the M1 Carbine was, which it likely won't be able to approach in weight, even with a muzzle brake. The only SMG around early in US participation in WW2 was the Thompson SMG which was heavier than the Garand. Though in the name of production/logistics ease they might just make a lightened carbine version of TTL's 6mm Garand and say 'good enough'. After all the Euros issued bolt actions to their rear area personnel and got along fine. Even their SMGs were heavier than the M1 Carbine, so in lieu of an M3 Grease Gun at the time the US military might just do a carbine-d Garand, especially if the shortened barrel, folding stock 'tanker' Garand is viable. I'd imagine the Grease Gun shows up on time ITTL, just no M1 Carbine or BAR.

That would make things interesting post-WW2 vis-a-vis the NATO cartridge, as it is likely NATO just opts to adopt the 6mm cartridge and .30-06. If the Johnson LMG works out that might soldier on for a while, but perhaps the US does make an M60 in both 6mm and .30-06 in time for Vietnam.

As a counterpoint the report does mention that a .20 caliber round would be ideal out to 500 yards due to it's flat trajectory and low recoil and potential to be very lethal at high speeds, so perhaps OTL .30 Carbine becomes TTL's .20 Carbine. It would be somewhat similar to the .204 Ruger (which has an insane 250m zero!), though considerably less powerful and therefore lighter and much lower recoiling. A M1 Carbine then could be even lighter than IOTL and fully controllable in automatic, plus a 30 round magazine would be pretty necessary in that case. A folding stock version would entirely replace the SMG as a weapon and be vastly cheaper than the Thompson and potential cheaper than even the Grease Gun if it eliminates the .45 caliber entirely and with it the M1911. As it was the paratrooper M1 Carbine with folding stock had a holster like a large pistol:
View attachment 493532

In that case goodbye tanker Garand.

Very, very interesting. I will ponder this one. You dug up some fun alternative firearm possibilities for us.

 

[MichaelWest]

Be that as it may, that won't change the Army decision makers minds in the relevant time period. And the main reason given for not switching calibers, was the sheer amount of ammunition in storage in the .30-06 caliber. That will still be a primary consideration when evaluating a new caliber.

So for those considering a no USA in the great war scenario, other butterflies caged, we have no such stocks of ammunition and no drag upon the decision making. We might then see some more bold thinking?

 

[SsgtC]

So for those considering a no USA in the great war scenario, other butterflies caged, we have no such stocks of ammunition and no drag upon the decision making. We might then see some more bold thinking?

Possibly. Even in OTL, the army was poised to switch to .276 from the .30-06 for the Garand. It was only halted and the M1 ordered in .30-06 because of the massive stocks of bullets in that caliber. Perhaps if the Army was also considering a new MG and BAR replacement the switch in caliber wouldn't be seen as being nearly as disruptive?