Testing, testing...

[Tony Williams]

The plastic case technology you called our attention will make a huge difference and, and one could forecast, reduce the pressure to replace the 7.62X51 machine gun in the heavy dismounted role.

That depends on how the plastic-cased technology is introduced. One thing is for sure - both the guns and ammo will require entirely different manufacturing techniques than are used at present, so there's no particular advantage in retaining an existing calibre: they could and should start with a clean sheet.

The second point is that there isn't and never will be any relaxation of the pressure to reduce the weight of portable equipment and consumables (like ammo) so if the Army can get long-range performance comparable with the 7.62mm but with lighter ammo, they're likely to go for as much saving as possible. Which takes us back to a 6.5 to 7mm round.

We (especially me) keep forgetting that we live in a combined arms world. There was a recent (History, History International, or Discover Channel - I don't remember which) segment on the Barret rifle development, history and future plans. They appear to have implemented a variant of their M-107 that uses the 25 mm grenades developed, IIRC, for the now defunct OICM family of weapons.

True -- a 16-20 lb weapon and even heavier ammunition may be challenging to lug around, but the developments are there and will affect the 1 km game. These developments show possibilities. E. g., I remember seeing discussions on the web (~5 years ago) featuring an experimental UK guided 12 gauge round.

I don't doubt that we will see developments in weapon systems (my favourite idea is here: http://www.quarry.nildram.co.uk/MetalStorm.htm ) but there will always need to be rifles for precision targeting with minimal risk of collateral damage, which takes us back to the performance we want from these and therefore to the ammo...

When we factor that sort of thing into the assessment and are willing to accept one ammunition type (e. g. 85-90 gr 6.5) for box magazines and another (e. g. 115 to 130 gr 6.5 mm) for belted, while still maintaining the potential for interchangeability in emergencies, then a "one caliber" dismounted infantry solution appears feasible.

That could work in theory, but it seems to have a dubious history in practice. Both Spain and Japan introduced low-recoil versions of the 7.62mm NATO for rifle use, but these didn't seem to last. The Chinese also introduced light (assault rifle, LMG) and heavy (sniper rifle, GPMG) versions of their 5.8x42, but have begun to move towards a compromise "universal" loading instead. Maybe the complication is felt not to be worth it.