Why Oh WHy

[stanc]

In the article I posted, I don't think he says these would be useful for machine guns.

From the article: "...main battle cartridge able to carry the goods to 600-800 meters in a suppressive fire mode from a machine gun..."

He also wrote: "[6mm-223] should be able to drive an 85 grain bullet to 3000 fps. Its overall length, head size, case capacity, shoulder angle, etc. are identical to the current 5.56 NATO cartridge, so it could easily be adapted to current 5.56mm weapons merely by re-barreling."

The current 5.56mm weapons used by the US Army have a 14.5" barrel length. I doubt that 6mm-223 could push an 85gr bullet to anywhere near 3000 fps from a 14.5" barrel. Maybe 2600 fps, if that.

He followed with: "A FMJ 6mm bullet of boat tail spitzer form weighing 85 grains has an adequately high ballistic coefficient to make an excellent long range bullet..."

I don't know of any company that offers an 85gr FMJ, but Sierra has a 90gr FMJ that was developed specifically for the 6mm-223, and its BC is a mediocre 0.376 in the range of 2100-2800 fps.

Complicating matters further is that the article was written in 2002, long before lead-free bullets became mandated. Lead-free projectiles for 6mm-223 will either weigh less than 85gr -- and therefore have even lower BC, reducing long range capability -- or will have a much longer base, which will reduce powder capacity and muzzle velocity. This would be even worse for Tracer bullets, which are typically longer than Ball projectiles.

There was a time when I thought 6mm-223 would be a good alternative to 5.56x45 (http://www.benning.army.mil/magazine/200...6_pf01.pdf). But, it is just not the best option for an 800-meter cartridge.