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Seasoned Vet
 
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A key advantage of a bigger gun with more powder is better armor penetration. (as he stated the obvious.)
Go with God, but make Him walk the point.
If you load a mudfoot down with a lot of gadgets he has to watch somebody a lot more simply equipped - say with a stone axe - will sneak up and bash his head in while he is trying to read a Vernier. - Robert Heinlein
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Seasoned Vet
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quote:
Originally posted by rickdog
A key advantage of a bigger gun with more powder is better armor penetration. (as he stated the obvious.)
If you want armor penetration, then you want more powder with a bullet that has very high sectional density. The bullet needs to be long for it's diameter. The bullets with best sectional density and ballistic coeficient are usually around 6.5mm.
It is interesting to note that the US Military experimented with .27 NATO in the late 50's. It was a 6.65mm bullet in a necked down 7.62 NATO case. Here is a pic of some experimental 'universal' cartridges that were tried in the 1950's:
http://upload.sh0t.com/stuff/ExpRCAR+6.jpg
From L to R: 6.5mm Arisaka for scale (6.5x50SR), .276 Pedersen (7x51), .280/30 EM-2 (7x43), .27 NATO (6.65x51), 6.45 Swiss Pat.80 (6.45x48), .25 Winchester(6.35x48), .25/30NATO (6.35x51), 6.25 British (6.25x43 - case only), 6mm SAW (6x45)
It is also interesting to note that Remington makes a 6.5mm cartridge with a necked down 7.62 NATO case known as the .260 Remington.
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Regular Joe
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Actually, armour penetration is a trade off between velocity and weight for a given frontal area. IOW, it's going to depend on the intended range of the use of the AP round. A very light high velocity rd with a hard core(tungsten or DU) will penetrate better than a heavy rd at lower velocity, until the velocity drops( aka range). That's why I recommended a 100gn hardcore bullet for the 6.8 and just drive it faster. This will result in better armour penetration up close, which is about the only time I see the AP being really needed, to deal with hardplate class III&IV body armour, and maybe punch APC's and other LAV's at close range in a MOUT environment. Ball will do trucks, cars and other soft targets just fine IMO/IME.
Same niche as M993/M995, with performance of the 6.8x43 more towards the 7.62x51 AP, and with the 6.8mm GPMG round being of better performance. The 5.56 projectile weighes 52gn, and the 7.62mm projectile weighes 127gn, both significantly less than the service ball ammunition.
http://www.fas.org/man/dod-101/sys/land/m993.htm
This is the performance benchmarks to compare to:
The 5.56 AP round penetrates 12 mm armour plate of 300 HB at 100 m. The 7.62 AP round penetrates 15 mm armour plate at 300 m. It also penetrates 120 mm Plexiglas helicopter protection and is highly effective on brick and concrete walls and causes no barrel wear.
So the 6.8x43 could be said to perform similar to or better than the 5.56x45 AP, and the 6.8mm GPMG would perform better than the 7.62x51 AP. I'd expect the 6.8GPMG to do bad things to BMP's, BTR, BRDM's, etc at MOUT range(0-300m) from elevated positions(negating the advantage of armour slope). And I suspect it will push the requirements for hard armour resistance as well. S/F....Ken M
"It's easy to be hard, it's hard to be smart"
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Seasoned Vet
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Whenever fighting men have adopted personal armor, there has been a drive to penetrate the armor (duuh). The armor has always lost because it eventually got too heavy. I see mobility increasing in the future.
Go with God, but make Him walk the point.
If you load a mudfoot down with a lot of gadgets he has to watch somebody a lot more simply equipped - say with a stone axe - will sneak up and bash his head in while he is trying to read a Vernier. - Robert Heinlein
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Hard Charger
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The 6mm sounds a lot like the .280 that the Army was set to adopt before WWII. The story I heard (can't remember where) was that the new cartridge was superior in every way to the .30 US (.30-06 in civilian terms) but that its adoption was nixed by then-CSA Douglas McArthur as a cost-saving measure. McArthur reasoned that with millions of .30 rounds in storage and thousands of weapons already in existence for that caliber (M-1903 and M-1917 Rifles, M-1917 and 1919 Machine Guns and the B.A.R.) it would be too expensive to adopt the new cartridge. I'd even heard that a version of the M-1 Garand was actually made in the new, .280 caliber, but again rejected as a cost-saving measure.
So, I guess the more things change, the more they stay the same.
Martin  "When I'm in command, every mission is a suicide mission" - Zapp Branigan, Futurama
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Seasoned Vet
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quote:
Originally posted by martinjmpr
The 6mm sounds a lot like the .280 that the Army was set to adopt before WWII. The story I heard (can't remember where) was that the new cartridge was superior in every way to the .30 US (.30-06 in civilian terms) but that its adoption was nixed by then-CSA Douglas McArthur as a cost-saving measure. McArthur reasoned that with millions of .30 rounds in storage and thousands of weapons already in existence for that caliber (M-1903 and M-1917 Rifles, M-1917 and 1919 Machine Guns and the B.A.R.) it would be too expensive to adopt the new cartridge. I'd even heard that a version of the M-1 Garand was actually made in the new, .280 caliber, but again rejected as a cost-saving measure.
So, I guess the more things change, the more they stay the same.
Yes Martin, John C. Garand originally chambered his M-1 in .276 Pederson which is a 7x51mm cartridge. It held 10 rounds in the clip with this cartridge. After WWII, the Brits came up with several new 7mm intermediate cartridges such as the .270, the .280 (7x43mm), the .280/30, and eventually a 7x49mm cartridge. The US adamently rejected these for the full power 7.62x51mm T-65 cartridge that became 7.62mm NATO standard in 1955.
Check out this pic to see the .276 Pederson Cartridge, it is second from the left:
http://upload.sh0t.com/stuff/ExpRCAR+6.jpg
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Cherry
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Can the US military adopt one cartridge that would meet the needs of CQB, Main Battle Rifle, Precision Rifle and SAW?????,,, Yes.
To do so, don't loose sight of one very important idea of a one cartridge solution ----
1. You need one cartridge case in one caliber that can use different weight and construction bullets for the various missions.
2. Ideas of making two cartridges with the same caliber bullet is not a one cartridge solution.
It is clear that the 5.56 NATO does not have the performance for use in a one cartridge system and the 7.62 NATO will not work in the M16 platform and it suffers from heavy recoil and high ammunition weight that will only add to the load burden soliders currently face so neither one are a solution.
The 6.8 SPC is lighter and has less recoil then the 7.62 NATO, but it does not have the huevos for 1,000 yard use in precision rifle or the SAW. Therefore, it does not have the performance for use in a one cartridge system.
As you think in theory, keep in mind that the key to success of any one cartridge system is that it MUST work in the M16 in its various configurations, Precision Rifles and a SAW. The single cartridge can have different bullet weights and designs for various missions, but all ammunition must work in every platform if required.
Therefore, to meet these requires, the new cartridge must have a OAL of 2.255" to be able to work in the M16 and existing platforms must be able to be converted to it's use through an armorer conversion kit.
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