US Army Considers Adopting an Interim Battle Rifle in 7.62NATO: eventually adopt 6.5

[ahillock]

Going with 7.62 allows a long-range rifle to be fielded ASAP (and at lowest cost), instead of waiting years for the requisite .260 loadings to be developed, tested, approved, and produced in quantity so that a .260 rifle could enter service.

I would agree with this and was exactly what came to mind. Rather than wait for years and years of testing and other bureaucratic time wasting, it gives the Army the chance to get a long range rifle ASAP and at a fairly low cost as you mentioned. That also gives them the chance to do all the testing that needs to be done to move to .260 for long term use. That will take time, but at least in the meantime they would have the 7.62x51 to hold them over until that time point in the future.