The 277 Fury is a case similar in size to the 308 and the weight savings comes from the case having a steel casehead. What we are seeing is a modernized version of the M14 or a rifle similar in size and shape to a AR10. Ammo bulk and recoil will make it less easy to carry and shoot.
https://www.gunsamerica.com/digest/277-sig-fury-demystified/
https://www.gunsamerica.com/digest/277-sig-fury-demystified/