Grendel as a Universal Infantry Cartridge

[stanc]

I've always understood that as well, but there seems to have been consideration for a 1/9 rifling for the rifles.

IIRC, 1:9 was considered for rifles, since that twist is adequate to stabilize 62gr M855, while also providing better accuracy (than 1:7) with 55gr M193.

However, the decision makers were apparently knowledgeable enough to realize that small unit leaders and others often use tracer ammo for signalling, fire direction, etc, and so chose the 1:7 twist with that in mind. Good thing, too, as it enabled bullets like the 77gr MatchKing to be used in carbines and rifles.