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Gents,

I'm questioning the need for the 6.5 X 51mm over the 7.62 x 51mm. Most engagements are under 300 yards and, if longer, I would think the .308 could do the job without costing $2.00+ per round. Am I missing something here? I put this in the same category as the F-35. What do we really need?

Inquiring minds, etc...?

Wes
 

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Whats funny about this whole thing is that any ammo a civilian will be able to buy in this new caliber is the same darn thing as 7mm-08. A lot of hype for nothing unless you are able to acquire the ammo its designed to use to gain the benefits. I doubt Uncle Sam will allow the sale of overflow 80k psi ammunition.
 

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Seems like that switch barrel kit that Knights Armament had would be the ticket. 2 or 3 barrels cover 5.56/300BO to 300 WM.
 

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I'm questioning the need for the 6.5 X 51mm over the 7.62 x 51mm. Most engagements are under 300 yards and, if longer, I would think the .308 could do the job without costing $2.00+ per round. Am I missing something here?
What you are missing is the US Army report from the conflict in Afghanistan, which was written in 2008 or 2009. It showed that engagement distances for US Army infantry soldiers were in excess of 300 meters about half the time, and our soldiers could not effectively strike back at the enemy when they are shooting down at us from mountain cliffs (often with Russian PK light machine guns in 7.62x54R, etc). It also made note that US Infantry soldiers were already 'over-burdened' with their gear, and the high altitudes/mountains exacerbated the situation. FYI: there is no shortage of PK light machine guns used by the Taliban for the past 25 years...its effective range is 1000 meters, maybe a little more.
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It was determined that every US Army Infantry Squad needed at least one DMR soldier with a Squad Designated Markman rifle in caliber 7.62 NATO that could provide precise fire out to 600 meters. The M14 EMR-RI was quickly developed as a stop-gap to meet urgent Mission Need Statements, and Rock Island Arsenal quickly made 6200 of them from 2009-2012, thereby enough to equip all deployed US Army infantry squads with a unified configuration. When the war in Afghanistan drew down, the US Army had an open competition for a new 7.62 Squad Designated Marksman Rifle (SDMR). H&K won the contract and I think they have delivered approx 5000 to 6000 of those rifles, designated the M110A1, as a one-for-one replacement of the legacy M14 EBR-RIs.
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However, I think the US Army also realized that they needed to replace the old M249 light machine gun with something that provided a longer range, more kinetic energy down range, and preferably more accuracy. I think that is why the high-pressure, 6.8x51mm cartridge was developed with the hybrid case, etc. Hence the Next Generation Squad Weapons, which was won by SIG this year.

Problem: The effective range of the M249 Squad Automatic light machine gun was 600 or 800 meters, depending if area fire vs suppressive fire, and I think that spec is generous w/ generic M855 ammo. In contrast, the new XM250 Squad Automatic light machine gun with the new high pressure 6.8x51mm round at “over 3000 fps” - reportedly has an effective range of 1200 meters. The BC of the 135 grain bullet is reportedly (correction) .500, which is excellent for a standard infantry military bullet. That provides a significant advantage over the old M249, and presumably needed in combat against contemporary Russian and Chinese light machine guns, and the contemporary body armor of those soldiers. See my post #23 re the M249, which also has somewhat poor accuracy..

The XM5 infantry rifle may utilize a lower velocity/standard pressure 6.8x51mm round based on a recent US Army document. It refers to fielding a “reduced range” cartridge in fiscal year 2023. Why? Infantry soliders might not need such a powerful round in a light XM5 rifle with 13" or 16” barrel, but the much heavier, belt-fed XM250 light machine gun with its 24” barrel can utilize the high pressure 6.8x51mm round, which allows the 1200 meter effective range.

My opinion is the high pressure 6.8x51mm round with its hybird case and 80k PSI pressure level was designed primarily for a suppressed light machine gun they weighs 20 or so pounds. In contrast, the XM5 is more likely seen as a 600 meter rifle, which is twice the effective range of an M4 carbine with M855 ammo. (300 meter effective range). I think the XM5 rifle may use a new “downloaded” round that will be more controllable in full-auto, but is still usable in the XM250 if needed, but with reduced effective range, yet will still be able to penetrate the body armor of enemy soldiers. At least that is my impression.
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Translation: The high-pressure 6.8x51 cartridge gives the XM250 at the top a 1200 meter effective range for aimed/area fire. That is twice the effective range of the legacy M249 w/ 5.56mm ammo. The suppressor likely makes this rifle much more controllable.

The soon to be fielded 'reduced range' 6.8x51mm cartridge presumably gives the XM5 infantry rifle a 600 meter effective range for aimed fire. Again that is twice the effective range of the legacy M4 Carbine with M855 (5.56mm) ammo. Suppressor likely helps controllability of this light rifle.

Again, I think our experience in Afghanistan (and perhaps to a lesser extent Iraq) provided some lessons learned about what US Army Infantry soldiers need when fighting in wide open terrain... The US Army decided that neither an M249 (600/800 meter weapon) or an M4 w/ M855 (300 meter weapon) - provided enough effective range for infantry soldiers given this open terrain.
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Gents,

I'm questioning the need for the 6.5 X 51mm over the 7.62 x 51mm. Most engagements are under 300 yards and, if longer, I would think the .308 could do the job without costing $2.00+ per round. Am I missing something here? I put this in the same category as the F-35. What do we really need?

Inquiring minds, etc...?

Wes
Any different from the .260 Remington which has been around for quite awhile?
 

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The XM5 may be a 600 meter rifle but will our troops, with their limited marksmanship training, be able to effectively engage targets at that distance? The fundamentals of accuracy are the same, makes no difference if the rifle is scoped or with mechanical sights.
Yes, and hopefully the US Army will update its training to focus on marksmanship out to 600 meters with the new rifles, as opposed to 300 meters with the M4 Carbines. However, don't discount what a decent 1-6x optic can do for an infantry soldier’s ability for precision fire.

The Marines of course pay attention to individual marksmanship, but adding a 3.5x optic back in 2004 did make a big difference even for those trained riflemen:
"The ACOG mounted on the M16 service rifle has proven to be the biggest improvement in lethality for the Marine infantryman since the introduction of the M1 Garand in World War II.”
- Major General J.N. Mattis, Commanding General, 1st Marine Division, Operation Iraqi Freedom
 

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I don't understand this at all - so the enemies up in the mountains are using old worn AK47s...and we cannot engage w/ newer weapons? and at 300 yards? For petesakes - 300 yards is the sitting position w/ iron sights. We shoot the 200 yards offhand -

And every Dick and Sally has scoped rifles and cannot engage? What kind of rifle marksmanship have they been thru?

Someone explain this to me -
 
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What you are missing is the US Army report from the conflict in Afghanistan, which was written in 2008 or 2009. It showed that engagement distances for US Army infantry soldiers were usually in excess of 300 meters, and our soldiers could not effectively strike back at the enemy when they are shooting down at us from mountain cliffs. It was determined that every US Army Infantry Squad needed at least one DMR soldier with a Squad Designated Markman rifle in caliber 7.62 NATO that could provide precise fire out to 600 meters. The M14 EMR-RI was quickly developed as a stop-gap to meet urgent Mission Need Statements, and Rock Island Arsenal quickly made 6200 of them from 2009-2012, thereby enough to equip all deployed US Army infantry squads. When the war in Afghanistan drew down, the US Army had an open competition for a new 7.62 Squad Designated Marksman Rifle (SDMR). H&K won the contract and I think they have delivered about 6000 of those rifles, designated the M110A1, as a one-for-one replacement of the legacy M14 EBR-RIs.
View attachment 483381

However, I think the US Army also realized that they needed to replace the old M249 light machine gun with something that provided a longer range, and preferably more accuracy. I think that is why the high-pressure, 6.8x51mm cartridge was developed with the hybrid case, etc. Hence the Next Generation Squad Weapons, which was won by SIG this year.

Problem: The effective range of the M249 Squad Automatic light machine gun was 600 or 800 meters, depending if area fire vs suppressive fire, and I think that was spec generous w/ M855 ammo. In contrast, the new XM250 Squad Automatic light machine gun with the new high pressure 6.8x51mm round at “over 3000 fps” - reportedly has an effective range of 1200 meters. The BC of the 135 grain bullet is reportedly .400, which is decent for a standard military bullet. That is a significant advantage over the old M249, and presumably needed in combat against contemporary Russian and Chinese light machine guns, and the contemporary body armor of those soldiers. See my post #23 re the M249, which also has somewhat poor accuracy..

The XM5 infantry rifle may utilize a lower/standard pressure 6.8x51mm round based on US Army document. It refers to fielding a “reduced range” cartridge in fiscal year 2023. Why? Infantry soliders might not need such a powerful round in a light XM5 rifle with 16” barrel, but the much heavier, belt-fed XM250 light machine gun with 24” barrel can utilize the high pressure 6.8x51mm round.

My opinion is the high pressure 6.8x51mm round with its hybird case and 80k PSI pressure level was designed primarily for a suppressed light machine gun they weighs 20 or so pounds. In contrast, the XM5 is more likely seen as a 600 meter rifle, which is twice the effective range of an M4 carbine with M855 ammo. (300 meter effective range). I think the XM5 rifle may use a new “downloaded” round that will be more controllable in full-auto, but is still usable in the XM250 if needed, but with reduced effective range, yet will still be able to penetrate the body armor of enemy soldiers. At least that is my impression.
View attachment 483375
Translation: The high-pressure 6.8x51 cartridge gives the XM250 at the top a 1200 meter effective range for aimed/area fire. That is twice the effective range of the legacy M249 w/ 5.56mm ammo. The suppressor likely makes this rifle much more controllable.

The soon to be fielded 'reduced range' 6.8x51mm cartridge presumably gives the XM5 infantry rifle a 600 meter effective range for aimed fire. Again that is twice the effective range of the legacy M4 Carbine with M855 (5.56mm) ammo. Suppressor likely helps controllability of this light rifle.

Again, I think our experience in Afghanistan (and perhaps to a lesser extent Iraq) provided some lessons learned about what US Army Infantry soldiers need when fighting in wide open terrain...
I bet you turned in some kick ass book reports, if you found a book you liked.
 

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Actually it's a 6.8x51mm cartridge.
Basically, the Army wanted a cartridge that could defeat body armor at 500 meters.
140gr bullet at 3,000 FPS from a 16” barrel
At 500 yards (16" barrel)
CartridgeEnergyDrop
6.8x51mm1654 ft.lbf-41"
5.56x45mm404 ft.lbf-90"

They can produce up to 80,000 PSI because of steel head cartridge cases that the M5 will use.
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What you are missing is the US Army report from the conflict in Afghanistan, which was written in 2008 or 2009. It showed that engagement distances for US Army infantry soldiers were usually in excess of 300 meters, and our soldiers could not effectively strike back at the enemy when they are shooting down at us from mountain cliffs. It was determined that every US Army Infantry Squad needed at least one DMR soldier with a Squad Designated Markman rifle in caliber 7.62 NATO that could provide precise fire out to 600 meters. The M14 EMR-RI was quickly developed as a stop-gap to meet urgent Mission Need Statements, and Rock Island Arsenal quickly made 6200 of them from 2009-2012, thereby enough to equip all deployed US Army infantry squads. When the war in Afghanistan drew down, the US Army had an open competition for a new 7.62 Squad Designated Marksman Rifle (SDMR). H&K won the contract and I think they have delivered about 6000 of those rifles, designated the M110A1, as a one-for-one replacement of the legacy M14 EBR-RIs.
View attachment 483381

However, I think the US Army also realized that they needed to replace the old M249 light machine gun with something that provided a longer range, and preferably more accuracy. I think that is why the high-pressure, 6.8x51mm cartridge was developed with the hybrid case, etc. Hence the Next Generation Squad Weapons, which was won by SIG this year.

Problem: The effective range of the M249 Squad Automatic light machine gun was 600 or 800 meters, depending if area fire vs suppressive fire, and I think that was spec generous w/ M855 ammo. In contrast, the new XM250 Squad Automatic light machine gun with the new high pressure 6.8x51mm round at “over 3000 fps” - reportedly has an effective range of 1200 meters. The BC of the 135 grain bullet is reportedly .400, which is decent for a standard military bullet. That is a significant advantage over the old M249, and presumably needed in combat against contemporary Russian and Chinese light machine guns, and the contemporary body armor of those soldiers. See my post #23 re the M249, which also has somewhat poor accuracy..

The XM5 infantry rifle may utilize a lower/standard pressure 6.8x51mm round based on US Army document. It refers to fielding a “reduced range” cartridge in fiscal year 2023. Why? Infantry soliders might not need such a powerful round in a light XM5 rifle with 16” barrel, but the much heavier, belt-fed XM250 light machine gun with 24” barrel can utilize the high pressure 6.8x51mm round.

My opinion is the high pressure 6.8x51mm round with its hybird case and 80k PSI pressure level was designed primarily for a suppressed light machine gun they weighs 20 or so pounds. In contrast, the XM5 is more likely seen as a 600 meter rifle, which is twice the effective range of an M4 carbine with M855 ammo. (300 meter effective range). I think the XM5 rifle may use a new “downloaded” round that will be more controllable in full-auto, but is still usable in the XM250 if needed, but with reduced effective range, yet will still be able to penetrate the body armor of enemy soldiers. At least that is my impression.
View attachment 483375
Translation: The high-pressure 6.8x51 cartridge gives the XM250 at the top a 1200 meter effective range for aimed/area fire. That is twice the effective range of the legacy M249 w/ 5.56mm ammo. The suppressor likely makes this rifle much more controllable.

The soon to be fielded 'reduced range' 6.8x51mm cartridge presumably gives the XM5 infantry rifle a 600 meter effective range for aimed fire. Again that is twice the effective range of the legacy M4 Carbine with M855 (5.56mm) ammo. Suppressor likely helps controllability of this light rifle.

Again, I think our experience in Afghanistan (and perhaps to a lesser extent Iraq) provided some lessons learned about what US Army Infantry soldiers need when fighting in wide open terrain...
Excellent synopsis but given your numbers, what exactly does this new round do that 7.62 NATO hasn’t been doing for going on 3/4 of a century? The M4 and especially the 249 were mistakes for widespread adoption. The fix has always been a 20” barrel for the M16 which is of course, how it was originally designed. It’s a 550m weapon which is all you need as a rifleman. The fix for the 249 is the 240. The 240 fixes most anything and is worth every ounce of it’s heft. The 240 is everything the SAW is not; hard hitting, accurate, reliable, and easy to clean. There’s little weight and size difference between the new round and 7.62x51 so what’s the edge?
 

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Well other than what I already said about body armor, the 6.8 is supposed to shoot flatter and have more energy at 500 yards than the 7.62x51mm cartridge, even with a 24 inch barrel vs. a 16 inch barrel on the 6.8. Of course the actual M5 is supposed to have a 13" barrel which is why they wanted to push chamber pressures to 80,000 PSI, the higher pressures will push the bullet to the kinds of velocities and energies that they figure will be needed to penetrate high end body armor.

They claim that the cartridge was actually developed for the new M250 machine gun first and then they wanted a standard battle rifle that matched that cartridge.

This is just a change in cartridge capability based on the assumption that China and Russia will field body armor that can't be defeated at typical contact distances with our current weapons.
 

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The US Army has been going woke - and gender-fluid. Why not make the weapon gay too? First it was the 6.8 SPC and now this? So a more exotic brass and powder? I cannot imagine what the new pistol will look like. 😁

There is nothing wrong w/ the 7.62 NATO. They had already fielded a newer tip for it -armor piercing. What is wrong w/ that? I got some of them awhile back from a friend. Very nice rounds. Only issue was it may chew up the chamber over time of use.

This is just so terrible.
 

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The US Army has been going woke - and gender-fluid. Why not make the weapon gay too? First it was the 6.8 SPC and now this? So a more exotic brass and powder? I cannot imagine what the new pistol will look like. 😁

There is nothing wrong w/ the 7.62 NATO. They had already fielded a newer tip for it -armor piercing. What is wrong w/ that? I got some of them awhile back from a friend. Very nice rounds. Only issue was it may chew up the chamber over time of use.

This is just so terrible.
You seem a little too passionate about something that doesn’t affect your life in any way, shape, or form. If you look at raw numbers, the new full sauced version of 6.8x51 is ballistically superior to 7.62NATO in every way. If it gives an edge to our guys over their adversaries then why not?
 

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This warrants repeating as folks are too focused on the XM5 rifle and not focusing enough on the XM250 belt-fed Squad Light Machine Gun - which was likely Big Army’s focus - and why the high pressure 6.8x51mm round was initially developed.

They claim that the cartridge was actually developed for the new M250 machine gun first and then they wanted a standard battle rifle that matched that cartridge.
I’ll dig up the Army reports when I have a chance, but as others have noted, the new 6.8x51mm simply shoots much further, flatter, and delivers more energy than a typical 7.62 NATO round like M80. The 135 grain aerodynamic bullet has a G1 BC of .500, so wind deflection is quite good and is equivalent to legacy 7.62 Sniper ammo (M118LR and Mk 316 Mod 0). However, the velocity advantage of the 6.8x51mm is not trivial. The hybrid case allows considerably more pressure than a standard brass case.

Even the best 7.62 sniper ammo, the Mk 316 Mod 0, has a max effective range of 1000 meters. It will never be a 1200 meter cartridge, given the pressure limitation of 60k PSI for a standard brass case. Obviously one can not equip all infantry soldiers with carefully manufactured/expensive sniper grade ammo either. It’s also not appropriate to use sniper ammo in a full-auto machine gun.

Time will tell about the new 6.8x51mm cartridge. Clearly the Army wants to standardize on one caliber for both the belt-fed, Squad light machine guns, and the infantry rifles. My guess is the belt-fed M250 will be used with the easily identifiable high-pressure ammo (steel case head), and the M5 infantry rifle will be used with standard pressure ammo (standard brass case), but in urgent situations - either weapon can use either ammo interchangeably and safely. I will also speculate that those sound suppressors will definitely be needed whenever the high pressure ammo is used for both weapon controllability in full auto, and greatly reduced muzzle blast. Otherwise it will be painful to shoot that full-mojo ammo, esp in a lightweight, short-barreled M5.

BTW, the US Army, USMC, and Navy NSW, have all moved away from 7.62 NATO for “school-trained” snipers, and mostly use the 300 WinMag, aka Mk 248 Mod 1, which has a 1500 meter effective range. I suspect that was another lesson learned from the wide open spaces of Afghanistan and Iraq…
 

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I don't understand this at all - so the enemies up in the mountains are using old worn AK47s...and we cannot engage w/ newer weapons? and at 300 yards? For petesakes - 300 yards is the sitting position w/ iron sights. We shoot the 200 yards offhand -

And every Dick and Sally has scoped rifles and cannot engage? What kind of rifle marksmanship have they been thru?

Someone explain this to me -
Pop up, shoot back, targets force you to assume some very unorthodox shooting positions. The 100 lbs of gear you are wearing doesn't help any. The goal in the Infantry is to effectively engage the enemy before they are within range to effectively engage you. This goes back to the previous turn of the century, when every country sought the longest possible barrel with the longest possible bayonet.
 

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I am gonna refrain from further comments coz I am sure gonna offend the troops. If they think they need a new weapon - then im okay w/ that. If the brass thinks their troops need a new weapon just because... then that is very poor taste.
 
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Here's is what was apparently being used against US infantry in Afghanistan at ranges well in excess of 300 meters - Russian PK light machine guns in 7.62x54R, and some of the heavier 12.7mm machine guns as well. They are cheap and found in quantity over there. (I don't think the 300 meter AK-47 was the issue from the Army's perspective). At least that is what I recall from that 2009 Army report.
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This resulted in urgent Mission Needs Statement from field commanders, and ultimately this resulted in 7.62 NATO/M14 rifles being pulled from storage in a hurry, and once the conflict tapered off, resulted in a couple of new weapon systems being awarded contracts by the military. The new systems were/are designed to provide more lethality to standard US Army infantry units - and delivered at much further ranges...in fact, twice the effective range of the legacy M4 & M249 systems that will be replaced. Along with standard sound suppressors that likely enhance marksmanship, I suspect our troops will appreciate these newer systems. Hopefully that will be the case.
 
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