WI: M1 Garand designed around .250-3000 cartridge

[EverKing]

Here's an updated, more fair, comparison of some of rounds we've been discussing based on more accurate sources for the actual military loads (trajectories are all based on 1.5" sight height and Ballistic Coefficients all use Standard G1 Drag Function).

• Cartridge, Ball, Caliber .30 M1: 174.5gr, BC 0.167, SD 0.261, MV 2647. +2.9" @ 100yds, 0" @ 194yds, MPBR @ 225yds, -1186.08" @ 1000yds.
• Cartridge, Ball, Caliber .30 M2: 152gr, BC 0.125, SD 0.227, MV 2805. +2.9" @ 100yds, 0" @ 192yds, MPBR @ 220yds, -1587.79" @ 1000yds.
• Cartridge, Caliber 5.56mm, Ball, M855: 62gr, BC 0.151, SD 0.176, MV 2875. +2.83" @ 100yds, 0" @ 205yds, MPBR @ 236yds, -1200.02" @ 1000yds.
• ATL 6.35x48mm NATO Ball: 120gr, BC 0.350, SD 0.258, MV 2500. +2.88" @ 100yds, 0" @ 206yds, MPBR @ 241yds, -580.22" @ 1000yds.

Ballistic Coefficients for the .30-06 M1 and M2 are calculated using JBM Online BC Calculator using the comparison of MV and 26 yard velocity from This Page.

Data for the M855 was copied from a comparison someone else had generated between it, the Mk.262, and the .300 BLK.

Ballistic Coefficient for the 120gr 6.35mm is estimated by splitting the difference between the Sierra 120gr HPBT which, considering it is a boattail, is likely worse than a FMJ military ball would be. A flatbased 120gr .25 caliber bullet is coming in at BC of 0.328 and the Speer 120gr Spitzer Boattail is showing 0.480! I chose the .35 because it seemed an adequate compromise (the .48 seems overly optimistic).

Here is the compared trajectories and details out to 1500 yards.

 

[Deleted member 1487]

Here's an updated, more fair, comparison of some of rounds we've been discussing based on more accurate sources for the actual military loads (trajectories are all based on 1.5" sight height and Ballistic Coefficients all use Standard G1 Drag Function).

• Cartridge, Ball, Caliber .30 M1: 174.5gr, BC 0.167, SD 0.261, MV 2647. +2.9" @ 100yds, 0" @ 194yds, MPBR @ 225yds, -1186.08" @ 1000yds.
• Cartridge, Ball, Caliber .30 M2: 152gr, BC 0.125, SD 0.227, MV 2805. +2.9" @ 100yds, 0" @ 192yds, MPBR @ 220yds, -1587.79" @ 1000yds.
• Cartridge, Caliber 5.56mm, Ball, M855: 62gr, BC 0.151, SD 0.176, MV 2875. +2.83" @ 100yds, 0" @ 205yds, MPBR @ 236yds, -1200.02" @ 1000yds.
• ATL 6.35x48mm NATO Ball: 120gr, BC 0.350, SD 0.258, MV 2500. +2.88" @ 100yds, 0" @ 206yds, MPBR @ 241yds, -580.22" @ 1000yds.

Ballistic Coefficients for the .30-06 M1 and M2 are calculated using JBM Online BC Calculator using the comparison of MV and 26 yard velocity from This Page.

Data for the M855 was copied from a comparison someone else had generated between it, the Mk.262, and the .300 BLK.

Ballistic Coefficient for the 120gr 6.35mm is estimated by splitting the difference between the Sierra 120gr HPBT which, considering it is a boattail, is likely worse than a FMJ military ball would be. A flatbased 120gr .25 caliber bullet is coming in at BC of 0.328 and the Speer 120gr Spitzer Boattail is showing 0.480! I chose the .35 because it seemed an adequate compromise (the .48 seems overly optimistic).

Here is the compared trajectories and details out to 1500 yards.

Are you using G1 BC for the 6.35mm and G7 for the rest? That is the only way you can have a .167 BC for the M1 Ball and .350 for the 6.35mm despite it having worse SD. It's not really a direct comparison then. Using the G7 BC on the table you did with the G1 model gives a vastly skewed table.

I'm getting a G1 BC for the M2 Ball as .405 not .125:
https://en.wikipedia.org/wiki/.30-06_Springfield

The .30-03 case was modified to have a slightly shorter neck to fire a spitzer flat-based 150-grain (9.7 g) bullet that had a ballistic coefficient (G1 BC) of approximately 0.405, a muzzle velocity of 2,700 ft/s (820 m/s), and a muzzle energy of 2,429 ft⋅lbf (3,293 J).

That's much better than the G1 of any of the .250 bullets.

The M1 Ball:

For these reasons, in 1926, the ordnance corps, after extensive testing of 7.5×55mm Swiss GP11 projectiles provided by the Swiss developed the .30 M1 Ball cartridge loaded with a new improved military rifle (IMR) 1185 propellant and 174-grain (11.3 g) bullet with a 9° boat-tail and an ogive of 7 calibers nose cone that had a higher ballistic coefficient of roughly 0.494 (G1 BC)

Again quite dominating compared to the 125 grain .250 bullets.

 

[EverKing]

Are you using G1 BC for the 6.35mm and G7 for the rest?

Oops, no I was using G1, but accidentally left the scale in feet instead of yards and I realized that the preset info for the M855 was in G7--thanks for keeping me honest! Ifound a more accurate G1 BC for the M855 of .304. In light of this, I have decided to be most fair I would split the difference between the 120gr HPBT and the 120gr SPBT for the 6.35mm, giving us .41.

Here is the corrected data:

And the link to the full graphs and chart.

Also, here is a quick comparison of weights (estimated for the 6mm SAW and 6.35 NATO) and recoils (assuming a 7.5 lbs rifle for all, just to give a fair comparison):

EDIT: Load data for the OTL Military cartridges in the above table are from Here.

 

[Deleted member 1487]

Oops, no I was using G1, but accidentally left the scale in feet instead of yards and I realized that the preset info for the M855 was in G7--thanks for keeping me honest! Ifound a more accurate G1 BC for the M855 of .304. In light of this, I have decided to be most fair I would split the difference between the 120gr HPBT and the 120gr SPBT for the 6.35mm, giving us .41.

Here is the corrected data:
View attachment 448731

And the link to the full graphs and chart.

Also, here is a quick comparison of weights (estimated for the 6mm SAW and 6.35 NATO) and recoils (assuming a 7.5 lbs rifle for all, just to give a fair comparison):

View attachment 448730

EDIT: Load data for the OTL Military cartridges in the above table are from Here.

Looking at that all of that the 6.35 Savage doesn't come off nearly as well as the 5.56, while the 6mm seems to split the difference of the 5.56 and 6.35.

 

[EverKing]

Looking at that all of that the 6.35 Savage doesn't come off nearly as well as the 5.56, while the 6mm seems to split the difference of the 5.56 and 6.35.

I agree the 6mm may be a little easier than the 6.35mm for the average grunt to handle but it isn't nearly so a big a difference that I could see Congress approving the expense and time it would take to make the switch--especially when there could be a possibility of simply improving the 6.35mm. Remember, we are basing the performance on low-end assumptions of velocity (.250-3000 handloads can get 120gr over 2600 fps with better powders, etc) and high end for weight.

As for the 6.35 vs. 5.56, the Trajectories don't seem that much different, sure, and the 5.56 has a definite weight and recoil advantage...but there are other factors that aren't included in those simple data: momentum, killing power, CQB capabilities, AP capabilities, etc. The 6.35 high SD form gives a marked advantage over the 5.56 in these areas. One way to look at it would be to use a "Killing Power Score" that some hunters use to better compare the capability of different rounds and calibers and their suitability for certain game types. It is a value calculated by the product of the Energy, Sectional Density, and Cross-sectional Frontal Area of the bullet. Using this formula and the published x-sectional area for the effected calibers, I came up with the following KPS scores (in 100 yard increments) of the four rounds compared in the trajectory charts:

Since I haven't calculated the energies for the 6mm I did not include that one.

Comparing the 6.35mm to the 5.56mm we can get the following:

• Weight of Ammunition: 154%
• Felt Recoil Energy: 237%
• KPS @ 0: 285%
• KPS @ 400: 355%
• KPS @ 1000: 449%

What this means is that the 6.35mm in only 54% heavier, with just over double the felt recoil--but within normal battle ranges it is has roughly three times the stopping power and the difference just increases with range. To put it another way, the 6.35 has the same theoretical effectiveness at 1000 yards as the 5.56 has at about 300 yards.

I am by no means saying the .250-3000 is the perfect all-purpose round for Military use. I am just saying that it is in the ball-park of being so. I think if it had been adopted and well established prior to WWII and kept as the primary NATO round in the first few decades of their existence it would be hard to justify switching to anything else in 6-7mm range because the benefits would be so minor and the change so expensive. 5.56mm may still be adopted as some sort of light carbine round but if we already kept a full length .30-.32 caliber for MMG and sniper use (such as a NATO standardized .30-06 or 7.92x57mm) they would hesitate to adopt a third standard round--which is what killed the 6mm SAW IOTL.

 

[Deleted member 1487]

I agree the 6mm may be a little easier than the 6.35mm for the average grunt to handle but it isn't nearly so a big a difference that I could see Congress approving the expense and time it would take to make the switch--especially when there could be a possibility of simply improving the 6.35mm. Remember, we are basing the performance on low-end assumptions of velocity (.250-3000 handloads can get 120gr over 2600 fps with better powders, etc) and high end for weight.

As for the 6.35 vs. 5.56, the Trajectories don't seem that much different, sure, and the 5.56 has a definite weight and recoil advantage...but there are other factors that aren't included in those simple data: momentum, killing power, CQB capabilities, AP capabilities, etc. The 6.35 high SD form gives a marked advantage over the 5.56 in these areas. One way to look at it would be to use a "Killing Power Score" that some hunters use to better compare the capability of different rounds and calibers and their suitability for certain game types. It is a value calculated by the product of the Energy, Sectional Density, and Cross-sectional Frontal Area of the bullet. Using this formula and the published x-sectional area for the effected calibers, I came up with the following KPS scores (in 100 yard increments) of the four rounds compared in the trajectory charts:

View attachment 448738

Since I haven't calculated the energies for the 6mm I did not include that one.

Comparing the 6.35mm to the 5.56mm we can get the following:

• Weight of Ammunition: 154%
• Felt Recoil Energy: 237%
• KPS @ 0: 285%
• KPS @ 400: 355%
• KPS @ 1000: 449%

What this means is that the 6.35mm in only 54% heavier, with just over double the felt recoil--but within normal battle ranges it is has roughly three times the stopping power and the difference just increases with range. To put it another way, the 6.35 has the same theoretical effectiveness at 1000 yards as the 5.56 has at about 300 yards.

I am by no means saying the .250-3000 is the perfect all-purpose round for Military use. I am just saying that it is in the ball-park of being so. I think if it had been adopted and well established prior to WWII and kept as the primary NATO round in the first few decades of their existence it would be hard to justify switching to anything else in 6-7mm range because the benefits would be so minor and the change so expensive. 5.56mm may still be adopted as some sort of light carbine round but if we already kept a full length .30-.32 caliber for MMG and sniper use (such as a NATO standardized .30-06 or 7.92x57mm) they would hesitate to adopt a third standard round--which is what killed the 6mm SAW IOTL.

I get what you're saying, but considering most rounds fired are for suppressive effect and you're probably not going to see someone in camo or at least dull colors in combat conditions at ranges over 300m without a scope, the potential killing power of the 6.35 at 400m and beyond is meaningless except for LMG/SAW or marksman/sniper use. In that context I agree that the 6.35 is certainly superior to the 5.56 M193 ball cartridge at ranges over 300m, but the KPS score is flawed because it doesn't account for the fragmentation effect the 5.56 has within 200m (or the effect the modern M855A1 has within it's effective range). So for the regular combat infantryman the 6.35mm cartridge is markedly inferior in most of the metrics that matter, but for special use it might be better and would have better penetration of cover. Still, it is then more likely just a replacement for the 7.62 with those used than of the 5.56. Also the 77 grain OTM 5.56 is apparently highly effective out to 800m in SAW and sniper use, which though the 6.35 might be more effective still have the recoil and cartridge weight penalties.

You are probably right that the 6.35mm Savage with higher pressure loads is close enough to the 6mm while maintaining an edge in certain areas to make it pointless to replace with 6mm SAW, however the 5.56 is different enough that it makes a lot of sense to still have as the basic infantry rifle cartridge and arguably DMR and SAW role. However for a modern LMG/maybe MMG a 'hot' 6.35 could well be the way to go with the proper bullet. I could see the .338 or .50 used for HMGs and special long range/anti-material sniping, but the 6.35 still having LMG/MMG use and regular sniper use.

Edit:
Also IOTL the AR-15 got the nod for army use because the defense department or rather McNamara forced it on the army after the M14 failed in Vietnam. So if TTL's M14 is in 6.35 and the rifle itself hits the same construction problems the AR-15 might well show up as per OTL, assuming the Air Force buys it like IOTL, which is may well might due to being light, low recoil, and shorter range and thus more suitable for base defense. So it might well win over the 6.35mm by accident, but given the surplus of 6.35mm rounds available and there being a bunch of 7.62x63 rounds for 'hmg' use (and all the left over weapons from WW2 and Korea), there well might be room for 3 different calibers (technically 4 due to the .50 M2). In WW2 though there were at least 4 different rounds in US, the .45 ACP, .30 Carbine, .30-06, and .50, plus the 9mm due to captured German weapons, so it isn't exactly unprecedented to have. The .30 probably wouldn't be around ITTL though and the .45 would get phased out whenever the US adopts the 9mm pistol/smg.

 

[EverKing]

5.56 is different enough that it makes a lot of sense to still have as the basic infantry rifle cartridge and arguably DMR and SAW role...

If I am understanding you correctly, you are saying let's improve the 6.35mm and get rid of the .30 MMG/Sniper; then slide the 5.56mm in underneath the 6.35 for DMR/SAW? I can get behind that. I think in the inter-bellum of the 70's-90's the military could move that way, possibly even adopting a 5.56 infantry rifle. However, in light of experiences with Counter-Insurgency and CQB in the War of Terror, I think the Military would soon move back to 6.35mm for the infantry rifle given the dissatisfaction many soldier have with the 5.56 in this role. In fact, it is exactly because of the CQB failings of the 5.56 that in the last 15+ years we have seen an explosion of new mid-caliber rounds: .300 BLK, 6.8 SPC, and the growing popularity and adoption of the 6.5 Creedmoor in the AR Platform, etc. They all try to accomplish what we already have built in ITTL with the 6.35x48mm NATO (albeit within the shorter OAL of the OTL AR15 lower receiver and magazine size, excepting the Creedmoor which has OAL equal to the 7.62x51mm and therefore fits in the AR10 platform instead).

 

[EverKing]

Here's an interesting article about the 5.56 that explains why it sometimes seems so impressive in combat and other times is completely in-effective:

http://abesguncave.com/why-556-223-is-both-the-best-and-worst-ar-15-cartridge/

 

[Deleted member 1487]

If I am understanding you correctly, you are saying let's improve the 6.35mm and get rid of the .30 MMG/Sniper; then slide the 5.56mm in underneath the 6.35 for DMR/SAW? I can get behind that. I think in the inter-bellum of the 70's-90's the military could move that way, possibly even adopting a 5.56 infantry rifle. However, in light of experiences with Counter-Insurgency and CQB in the War of Terror, I think the Military would soon move back to 6.35mm for the infantry rifle given the dissatisfaction many soldier have with the 5.56 in this role. In fact, it is exactly because of the CQB failings of the 5.56 that in the last 15+ years we have seen an explosion of new mid-caliber rounds: .300 BLK, 6.8 SPC, and the growing popularity and adoption of the 6.5 Creedmoor in the AR Platform, etc. They all try to accomplish what we already have built in ITTL with the 6.35x48mm NATO (albeit within the shorter OAL of the OTL AR15 lower receiver and magazine size, excepting the Creedmoor which has OAL equal to the 7.62x51mm and therefore fits in the AR10 platform instead).

Effectively yes. The 7.62 is in a weird spot because it is too light to really be good at anti-material work, sectional densities available that get good long range effect result in too much recoil to be ideal for rifles or lighter MGs, while larger calibers work better for the heavier MGs that can handle them without recoil concern. I'd even argue that the longest, heaviest 6.35mm bullets that can be stabilized in rifling in the 63mm .30-06 case might well get you where you want to be for a MMG/LMG/longer range sniper role, while the 5.56 would handle DMR/SAW/rifle roles just fine. You can leave either the .50 cal for HMG/long range sniping or do the .338 Magnum that is en vogue right now.

AFAIK currently the dissatisfaction with the 5.56 round was fixed with the move to the M855A1 bullet and the 77 grain heavy round, while the plans to adopt the 6.8mm (and maybe 6.5mm? Not clear on where that stands now) is more an issue of long range body armor penetration or fighting in Afghanistan mountains. For that the 6.35mm heavy round might be used in this ATL.

Ironically though in CQB the original 5.56 M193 bullet actually excelled heavily, because it's fragmentation effect was heaviest the closer to the muzzle the bullet hit the target at. As your link below notes at close range the 5.56 was king as proved in Vietnam.

None of the rounds you listed actually could compete with the 5.56 at close range, those rounds are mostly to be used at longer range, while the .300 blackout was based off of the Whisper series of bullets, which were meant to be used with a suppressor and maintain energy despite being slowed down to reduce noise signature. AFAIK right now though the M855A1 fixes all of the lethality issues of the M855

Here's an interesting article about the 5.56 that explains why it sometimes seems so impressive in combat and other times is completely in-effective:

http://abesguncave.com/why-556-223-is-both-the-best-and-worst-ar-15-cartridge/

There are a bunch of problems with this article, including that the AR-15 wasn't intended as a front line combat weapon. The Air Force didn't intend that, but the designers certainly did. It was also not designed for close range combat, it was designed to penetrate helmets out to 500m, which it did in a 22 inch barrel, but that was shortened in the final design...but then they were designed around the idea that all infantry rifle combat happens within 300m per operations research done in WW2 and Korea. Plus the fragmentation effect was not understood early on and they thought that the damage was resulting from tumbling (it sort of was, but it was the tumbling that induced fragmentation in the small bullets). Also the M855 round was designed around not fragmenting and in fact being a super penetrator due to the need to fight Soviet mechanized infantry in body armor at 600m, plus have a SAW bullet capable of remaining effective over 500m.

Of course he does not talk about the modern and current EPR M885a1 bullet, which is a three piece round that breaks apart at all velocities; if it hits you you're in trouble and it will punch through up to class III body armor while being relatively barrier blind. He references the 77 grain match bullet, which isn't specifically designed to fragment (it will in most cases) but rather to be effective out to 800m from sniper rifles...which gives them the ability to actually place bullets in highly damaging areas of the body negating the need for fragmentation effect unlike regular infantry who are often limited to putting rounds in the general direction of the enemy and hoping for the best.

 

[EverKing]

The 5.56 I would say can achieve devastating fragmentation but I would hardly call it king. The US Military recognizes that it is failing to achieve its goals even after continual attempts at improving the ammunition (including the M855a1). It achieves good fragmentation in tests but soldiers, marines and operators in the field give it mixed reviews and dissatisfaction with the round has been increasing in the last 10-15 years.

Begining this summer the DoD will begin field testing a newly developed 6.8mm round which is planned to replace all the 5.56 over the next decade or so. I think that is proof enough that while the 5.56 is adequate it has not lived up to expectations.

ITTL, again, if the 5.56 is adopted even in a limited role (security, SAW, etc) for a decade or two, I think the problems revealed with the early versions may convince the Brass that they are better off just keeping the 6.35mm standard instead of having to spend more money in continual attempts at improving yet another round. I think they will have their hands full enougheoptimizing the 6.35. It is very possible that by the 80s or 90s they are ready to look at a new Universal cartridge but I think the 5.56 would not be that cartridge.

 

[Deleted member 1487]

The 5.56 I would say can achieve devastating fragmentation but I would hardly call it king. The US Military recognizes that it is failing to achieve its goals even after continual attempts at improving the ammunition (including the M855a1). It achieves good fragmentation in tests but soldiers, marines and operators in the field give it mixed reviews and dissatisfaction with the round has been increasing in the last 10-15 years.

Do you have a source for that? I haven't been able to find what you mean. The claimed dissatisfaction seems to be with the longer range performance, not short range, especially related to the fighting in Afghanistan and the potential to piece body armor at longer ranges. Which is why the army adopted the 'magnum' 6.8mm round (not the 6.8 SPC) at the end of last year.
There have been a number of efforts by SOCOM forces to have larger caliber bullets, but AFAIK none have been officially adopted.

Begining this summer the DoD will begin field testing a newly developed 6.8mm round which is planned to replace all the 5.56 over the next decade or so. I think that is proof enough that while the 5.56 is adequate it has not lived up to expectations.

The 'magnum' 6.8mm round they adopted is for longer ranges and body armor piercing.
https://www.militarytimes.com/news/...cs-will-make-soldiers-marines-a-lot-deadlier/

The Next Generation Squad Weapon program aims to bring a new caliber that will reach farther, hit harder and do so with greater accuracy. At least initially, the M16/M4 will stick around, as the new weapon is geared for close combat units such as infantry, scouts and special operations.

“This is a weapon that could defeat any body armor, any planned body armor that we know of in the future,” Army Chief of Staff Gen. Mark Milley told Military Times. “This is a weapon that can go out at ranges that are unknown today and that you can see accurately. There is a target acquisition system built into this thing that is unlike anything that exists today. This is a very sophisticated weapon, and we think it’s very resilient. It will stand all the rigors of weather, terrain, and soldier use, and all of that kind of stuff. This is a pretty impressive gun.”
.....
In 2015, the Small Arms Ammunition Configuration Study showed similar results, pointing to an intermediate caliber as the best option. But the study pushed for higher muzzle energy for extending range and lethality at impact, while maintaining bearable recoil and consistent accuracy.
....
He highlighted adversaries’ use of 7.62mm weapons within their infantry units, which overmatched the U.S. 5.56mm weapons.
....
While the weapon extends ranges for the individual soldier beyond the current M4, from 300 meters to 600 meters, it does not change the fundamentals of marksmanship training.
....
Likewise, ranges are often limited in urban environments, though the increased power and barrier penetration of the 6.8mm will give shooters better options against certain urban obstacles.

So it's more about overmatch and keeping pace with the range of enemies using PK MGs and Dragunov sniper rifles from elevated positions. Plus without the limitations of iron sights and through laser rangefinding the accuracy issues that conscript infantry faced in WW2, Korea, and Vietnam it makes less sense in the 21st century to be limited to 300m effective combat range.

ITTL, again, if the 5.56 is adopted even in a limited role (security, SAW, etc) for a decade or two, I think the problems revealed with the early versions may convince the Brass that they are better off just keeping the 6.35mm standard instead of having to spend more money in continual attempts at improving yet another round. I think they will have their hands full enougheoptimizing the 6.35. It is very possible that by the 80s or 90s they are ready to look at a new Universal cartridge but I think the 5.56 would not be that cartridge.

Thing was it wasn't a problem in Vietnam for the most part, in fact it was a boon. The push recently to replace the 5.56 is more a function of the maturing of technologies that remove the barriers that affected accuracy or even just ability to see the target at longer ranges, plus the spread of body armor in peer level opponents that could stop even improved 5.56mm rounds. But as we see through the testing of the modern 6.8mm round, even the 6.35mm round could well be too weak for the role envisioned above. I agree that by a certain point the military would be looking at a bigger round, so perhaps they might have been better off adopted at least a 6.5mm round and sticking with it through the 20th century.

The 1980s-90s is not really the point they'd be looking for that though given the collapse of the USSR and lack of Class IV body armor being an issue. The 2010's have opened up a lot of new technologies that had made it clear that there will need to be a new infantry rifle paradigm, but just looking at the history of small arms development to the end of the 20th century the focus was still on the lighter rounds. Through the 1970s they were still actively testing the microcaliber rounds before deciding the cost of adopting a new caliber wasn't worth it without at least a doubling of capabilities over existing models. Apparently adopting the largest caliber possible while maintaining manageable recoil is ultimately where they ended up, I'm guessing in part due to the maturing of telescoping case technology, which keeps weight of the rounds down so they could still carry as many as standard 5.56.

 

[marathag]

while the .300 blackout was based off of the Whisper series of bullets, which were meant to be used with a suppressor and maintain energy despite being slowed down to reduce noise signature

When supersonic loads are used, ends up being a slightly less powerful .30-30 that has been a more than adequate Deer round out to 150-200 yards, just like the .250 Savage was.

 

[tomo pauk]

With 6.35mm in service, I don't see any impetus for the 5.56mm that might justify the expanse of whole military to switch to. Especially since the 6.35 would've received more than 50 years worth of technological improvements that ITTL went into 5.56.

 

[Deleted member 1487]

When supersonic loads are used, ends up being a slightly less powerful .30-30 that has been a more than adequate Deer round out to 150-200 yards, just like the .250 Savage was.

Yes, it approximates the performance of the 7.62x39, but that was a development of the original concept, which was to have a suppressable round usable from an AR platform. AFAIK the .300 supersonic blackout is not used by the military other than perhaps some SOCOM guys doing it as a personal choice.

With 6.35mm in service, I don't see any impetus for the 5.56mm that might justify the expanse of whole military to switch to. Especially since the 6.35 would've received more than 50 years worth of technological improvements that ITTL went into 5.56.

I didn't mean switch to entirely, just for the standard infantry rifle, with a LMG/SAW using the 6.35mm as well as DMRs and perhaps even an MMG. If anything what would be displaced is the 7.62, especially when .50 cal HMGs and anti-material sniper rifles arrive. The 5.56 offers certain benefits as of the 1950s-60s that something as large as the 6.35x48 could not that compete with, though the 6.35 does potentially offer a lot of advantages over the 7.62 even in 63mm.

 

[tomo pauk]

...
I didn't mean switch to entirely, just for the standard infantry rifle, with a LMG/SAW using the 6.35mm as well as DMRs and perhaps even an MMG. If anything what would be displaced is the 7.62, especially when .50 cal HMGs and anti-material sniper rifles arrive. The 5.56 offers certain benefits as of the 1950s-60s that something as large as the 6.35x48 could not that compete with, though the 6.35 does potentially offer a lot of advantages over the 7.62 even in 63mm.

'Just for the standard infantry rifle', like 80% of infantry firearms? Nope.
With 6.35mm accepted by 1930s, that round is used on:
- standard infantry rifle (semi- or full-auto)
- LMG
Also, with improved, post-war cartridge:
- DMR
- less need for 7.62, where the need for it is covered by .30-60 (plus left-over .303 in British and Commonwealth armies)

 

[Deleted member 1487]

'Just for the standard infantry rifle', like 80% of infantry firearms? Nope.
With 6.35mm accepted by 1930s, that round is used on:
- standard infantry rifle (semi- or full-auto)
- LMG
Also, with improved, post-war cartridge:
- DMR
- less need for 7.62, where the need for it is covered by .30-60 (plus left-over .303 in British and Commonwealth armies)

You sure it's 80%? That seems excessively high. And yes the advantages were that great that even over the 6.35x48 it would have been a huge improvement in critical areas at the time. Remember IOTL they tested a much smaller HV version of a 6.35x48 cartridge and the 5.56x45 beat it handily in the areas the military wanted. It took until the end of 2018 to finally unseat the 5.56 in future developments.

Now that said the 6.35x48mm upgraded from the Savage would have been pretty close to ideal as an LMG/SAW/DMR round. I'm not sure what role the 7.62 would have then, especially with the .50 cal being around and the end of 'barrage' firing of MGs.

 

[tomo pauk]

You sure it's 80%? That seems excessively high. And yes the advantages were that great that even over the 6.35x48 it would have been a huge improvement in critical areas at the time. Remember IOTL they tested a much smaller HV version of a 6.35x48 cartridge and the 5.56x45 beat it handily in the areas the military wanted. It took until the end of 2018 to finally unseat the 5.56 in future developments.

Check out the firearms of infantry in 20th century - they (the infantry) will lug around their Mausers, Springfields, Lee Enfields, Mosin-Nagants, Garands, SKSs, FALs, AK-47s, M-16s, bull-pups or not, fixed or folding stock, full size and with short barrel, in most of the cases.
5.56 was not firmly seated because it was the next best thing after sliced bread, but because nobody wanted to spend the cash to buy something better suited for longer ranges and with better penetration that also still can be controlled in automatic fire. We can recall that original US bullet (M193 was used in most of the cases in US Army) was supplanted with Belgian type, the SS109/M885, than again in the 21st century with M885A1 that also introduced greater pressures upon firing. There is no reason why the advancements in bullet technology cannot be applied to the .250, together with greater pressures for greater muzzle energy.
5.56 was widely criticized by US Army more than 15 years ago, once it was required by riflemen to return fire beyond 500m or thereabouts.

Now that said the 6.35x48mm upgraded from the Savage would have been pretty close to ideal as an LMG/SAW/DMR round. I'm not sure what role the 7.62 would have then, especially with the .50 cal being around and the end of 'barrage' firing of MGs.

7.62 could've still be useful for sniper rifles and vehicle-installed MGs. the .250 was perhaps 20% more powerful than early 5.56mm, for 800+m shoths it will not cut it that well.

 

[marathag]

There is no reason why the advancements in bullet technology cannot be applied to the .250, together with greater pressures for greater muzzle energy.

250 Savage was introduced at 42,000 psi, very respectable for 1915, while 5.56mm is over 60,000 now. Plus M16 when from 14:1 twist down to 7 to stabilize the heavier bullets

 

[Deleted member 1487]

5.56 was not firmly seated because it was the next best thing after sliced bread, but because nobody wanted to spend the cash to buy something better suited for longer ranges and with better penetration that also still can be controlled in automatic fire.

Read this before sticking to the above:
https://www.amazon.com/Black-Rifle-Retrospective-Modern-Military/dp/0889351155

We can recall that original US bullet (M193 was used in most of the cases in US Army) was supplanted with Belgian type, the SS109/M885, than again in the 21st century with M885A1 that also introduced greater pressures upon firing.

Sure, for a variety of reasons, namely the greater weight/longer bullet for longer range as well as greater armor penetrating ability to deal with body armor that was starting to show up in the Soviet military.

There is no reason why the advancements in bullet technology cannot be applied to the .250, together with greater pressures for greater muzzle energy.

Sure...which would increase recoil and wear and tear on the weapon, which is fine if taking on the roles the 7.62 took historically. Not so good for a standard infantry rifle until about now when the technology makes it possible to actually use it's potential.

5.56 was widely criticized by US Army more than 15 years ago, once it was required by riflemen to return fire beyond 500m or thereabouts.

The SS109/M885 were criticized. There wasn't a special requirement to fire at 500m really other than in Afghanistan. A 6.5mm or even potentially a 6.35mm round for DMR/LMG would have been just fine for that had the army not stupidly stuck to the 7.62.

7.62 could've still be useful for sniper rifles and vehicle-installed MGs. the .250 was perhaps 20% more powerful than early 5.56mm, for 800+m shoths it will not cut it that well.

Sure, but not enough more than the 6.35 to really justify it in a world where the .50 cal is in service and something like the .338 round is developed to deal with the inadequacies of the 7.62 caliber, but doesn't require the .50 cal.

The modern 77 grain 5.56 round is fine for 800m, the upgraded 6.35mm would be great over 1000m.

 

[tomo pauk]

Read this before sticking to the above:
https://www.amazon.com/Black-Rifle-Retrospective-Modern-Military/dp/0889351155

I've read a lot about 5.56 'effectiveness', including this.
US, British and German armies started incorporating plenty of guns in 7.62 NATO to remedy the situation.

Sure, for a variety of reasons, namely the greater weight/longer bullet for longer range as well as greater armor penetrating ability to deal with body armor that was starting to show up in the Soviet military.

In that they over-pressured the M4 from 52000 to 62000 psi, with much greater wear & tear on the weapon. Let's recall that .250 worked at 42000 psi, so there is a lot of headroom to improve it via increasing of pressure towards 50000-55000 psi.

Sure...which would increase recoil and wear and tear on the weapon, which is fine if taking on the roles the 7.62 took historically. Not so good for a standard infantry rifle until about now when the technology makes it possible to actually use it's potential.

See this: link.
A lot of wear & tear because of ammo pushing to 62000 psi.

The SS109/M885 were criticized. There wasn't a special requirement to fire at 500m really other than in Afghanistan. A 6.5mm or even potentially a 6.35mm round for DMR/LMG would have been just fine for that had the army not stupidly stuck to the 7.62.

US Army is not the only user of 5.56 ammo, not everyone was (re)fighting the Vietnam war with engagement ranges rarely beyond 300 m. 7.26 was needed to cover areas where 5.56 was not seen as useful: against targets beyond certain range, or/and against targets that have some sort of cover (behind vehicles, even non-armored, actual walls, logs + sand bags etc).

Sure, but not enough more than the 6.35 to really justify it in a world where the .50 cal is in service and something like the .338 round is developed to deal with the inadequacies of the 7.62 caliber, but doesn't require the .50 cal.

IIRC the machine guns in .338 are still very rare thing, I'm not sure they actually exist.
The .30-60 will offer twice the energy downrange vs. historical .250 ammo.

The modern 77 grain 5.56 round is fine for 800m, the upgraded 6.35mm would be great over 1000m.

I'd be satisfied with 1000 m.