Negative on that last. The Squad Automatic Weapon uses exactly the same ammunition as the service rifle M16A2-M4 series.
The old M16A1 used a 1-12" twist for the M193 Ball 55 grain ammunition. At the time of the adoption of the M16A2, the SAW was also adopted and the rifles and SAW required a faster twist rate (1-8") to stabilize the longer, heavier 62 grain bullets. SAW ammunition development required an 800 meter tracer capability, and the 5.56 x 45 NATO cartridge was stretched to make that. Both weapons are fully compatible with the current green-tipped ball ammo, and can still use the older M193 ammo with greatly diminished accuracy at long engagement ranges.
