here is a thread from thefiring line similar topic
http://www.thefiringline.com/forums/showthread.php?s=&threadid=128662&highlight=6mm+SAW
http://www.thefiringline.com/forums/showthread.php?s=&threadid=70695
Another informative article,
http://www.quarry.nildram.co.uk/Assault.htm
copied from the Kernel on The firing line
"...the best cartridge that never was."
The US Army has already spent the better part of a decade, thousands of man-hours, and millions of dollars developing a 6mm cartridge - arguably the ultimate small arm cartridge. It's sitting on the self ready to go but will probably never be adopted because of political and economic reasons. It's not the biggest, the fastest, or a magnum anything. It's a compromise of size, shape, weight, function, recoil, and energy. Perhaps the perfect compromise.
It's called the 6mm SAW - "the best cartridge that never was". It was developed in the early 70's and is officially known as the XM732 BALL. It was intended to be used with the (then experimental) Squad Automatic Weapon. SMALL ARMS OF THE WORLD, 12th Edition, by Ezell mentions the 6mm SAW briefly as it covers the development of the SAW machinegun in some detail.
The 6mm SAW was not derived from 5.56x45 or the 7.62x51 (or any other cartridge case for that matter), it's case dimensions are totally unique. According to CARTRIDGES OF THE WORLD, 8th Edition, by Barnes the OAL of a loaded round was 2.580". The case had a .410" head dia. and was 1.779" long. It was loaded with an extremely streamlined 105 gr bullet that moved out at 2520 fps from an 18" barrel, not that far behind cartridges like the .243 Winchester and 6mm Remington.
It wasn't just a pie-in-the-sky project. Development got pretty far, a lot of ammunition was even loaded in bulk at military arsenals. You might even turn one up at a big gun show if you scrounge around the cartridge collectors' tables. $5 a round last time I saw one.
One interesting facts about the 6mm SAW is it was the first cartridge to be designed by computer. The technique called "parametric design" was a complicated model of complex thermodynamic equations. The Army wasn't that impressed and once they figured out how to make tracers work in .223 caliber bullets they dropped the 6mm SAW. To bad in my opinion, the 6mm SAW had a lot going for it, and in civilian form the brass would have been the basis for many, many interesting cartridges that never will be.
Excerpt from Guns Review International, February 1996 by Anthony Williams
"....... in a series of experiments conducted by British, American and (possibly) Russian agencies to discover the ideal military small arms calibre. In the late 1960s, the Royal Small Arms Factory at Enfield began a detailed theoretical analysis of the striking energy needed to disable soldiers with various levels of protection, and the ballistics required to deliver that energy at battle ranges for a number of different calibres. The conclusion was that the optimum calibre would lie between 6mm and 6.5mm, and an experimental 6.25mm cartridge (based on the abortive 7mm round) was developed which was claimed to have significant advantages over both the 5.56mm and 7.62mm calibres. Performance proved to be virtually equal to the 7.62mm at up to 600 metres, with recoil and ammunition weight much closer to those of the 5.56mm.
At the same time, the US Army realised the need for a light machine gun with a longer effective range (out to 800 metres) than the 5.56mm cartridge could provide but appreciably less weight than the 7.62mm M60 MG. Their research led to the development of the 6mm SAW (Squad Automatic Weapon) cartridge. A relatively heavy bullet combined with a moderate velocity were selected for the optimum long-range performance. In the event, weapons firing improved 5.56mm ammunition were selected instead, largely to avoid the supply problems created by the use of three small-arms calibres. More recently, it has emerged that Russian armament firms, who had earlier copied NATO in producing a small-calibre (5.45mm) cartridge, are now offering weapons in a new 6mm calibre."
-- Kernel
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