En el campo de munición de arma larga militar, calibres como el 6.8x43 mm SPC de Remington, el 6,5 Grendel de Alexander Arms... parecen aportar lo que le falta al 5,56x45 mm
El USSOCOM no parece muy contento con el 5,56, y parece decidido a experimentar con el 6.8x43 Rem SPC. El 5,56 es suficiente hasta los 300 metros, debiendo usar el 7,62x51 para mas de 300.
Hay informes de Irak donde se critica tanto a arma como calibre (M4 y M16).
Si se unificase todo en 6.8x43 mm SPC o 6,5 Grendel es posible tener un calibre mas polivalente.
"This is the 6.8x43 Remington SPC (Special Purpose Cartridge) which fires a 115 grain bullet at 2,650 fps from a 16.5 inch barrel (7.45g at 808 m/s = 2,430j); very similar to the "ideal" 6.85mm listed above. The cartridge case is based on the old .30 Remington commercial round, with a larger diameter than the 5.56x45 to increase the case capacity. This round develops 55% more muzzle energy than the 62 grain SS109/M855 loading at the muzzle, rising to 84% better at 550m due to its superior ballistic coefficient. The trajectory precisely matches that of the 7.62x51 ball out to 500m, and is only 10cm low at 600m."
http://www.defensereview.com/modules.php?name=News&file=article&sid=383