Constant recoil, was not Sullivan or Stoner's idea, it was first seen in the MP-44

[BluntForceTrauma]

Klem, in general, the range concerns in AFG were that our troops were being ambushed by PKMs with 7.62x54R at, oh, 800 meters and couldn't adequately respond with 5.56. Thus the push for the increased ballistic capability of the 6.8 NGSW to both have long range external ballistics as well as body armor defeat at those ranges.

Here's a quick ARTICLE from which I quote: "We’re looking to reach out around 600 meters and have lethal effects even if the target is protected by body armor,” Col. Geoffrey A. Norman, force development division chief at Army HQ, told Task & Purpose at the time. “We need to have lethal effects against protected targets and we need to have requirements for long-range lethality in places like Afghanistan, where you’re fighting from mountaintop to mountaintop over extended ranges.”