If you are referring to the original Squad Automatic Weapon project from many years ago, I am not sure. The original 6mm SAW used the existing 5.56mm (.223 Rem) case.
Around the same time many folks were experimenting with wildcating the same case for use in Thompson Center pistols and they were used in .257, .264, .277 .284 and .30 diameter with the .264 and .284 becoming actual calibers, 6.5 and 7mm TCU. There is also the little .25 Wooters which is the same thing in .257 but it remains a wildcat. Actually the .300 Whisper is a quasi-factory round, I think Cor-Bon actually ran some.
Of late on Special Forces Group has experimented with bigger cases from the .30 Rem to the .220 PPC in a wide variety of cases. Their recommendation ended up with the experimental adoption and actual issue of M4s in 6.8 SPC.
Indepentendly, Alexander Arms has been floating the "6.5 Grendel" which is a modified 6mm PPC case pushing .264 bullets.
Lots of stuff out there!