Testing, testing...

[Tony Williams]

Hmm. That's just the reverse of what I got from your "bite the bullet" article and presentations.

True, but the situation continues to evolve. The widespread distribution of 7.62mm rifles and MGs down to section level (helped by the fact that the British have just joined the US in selecting the 7.62mm Minimi) has to a large degree addressed the range and (to some extent) the effectiveness issues of 5.56mm, but has created a new problem - ammo weight!

That's what I used to think, too. However, with the switch from SAAMI to the Spec II chamber, 6.8 SPC is looking much better than it did. Muzzle velocity with bullets of the same weight and type, 6.8 SPC outdoes 6.5 Grendel by 200-300 fps. Since a new carbine/rifle/LMG need not have the M16 mag well dimensions, neither does cartridge OAL have to be 2.25 inches of the 5.56 round. Let cartridge length be 2.40 inches, and 6.8 SPC can use very streamlined bullets. Combined with the higher velocity, and now 6.8 SPC might not only equal 6.5 Grendel at long range, it might even beat it.

I wouldn't argue with that: my suggested ideal cartridge in calibres between 6.5mm and 7mm is based on the 6.8 Rem case, but slightly longer, and with space for a much longer bullet. In terms of conventional ammunition technology, I think this could represent the ideal dimensions and proportions.

If we were sticking to lead+steel cored bullets I would choose 6.5mm as the ideal calibre, but with copper+steel (or even just steel) bullets as seems mandatory nowadays, getting sufficient weight within a reasonable length becomes a problem for long, VLD bullets. So I am agnostic over the exact calibre, it all depends on how the sums work out; the answer could be 6.8mm or even 7mm.

I'm skeptical of that. The only real data we have to go on is for the 120gr Norma FMJ, which has a 0.428 BC. That's far below the 0.54 BC of the 123gr Scenar. I just don't see the BC of a 120gr FMJ getting above 0.44-0.45, and 110gr is said to be the "sweet spot" for this cartridge -- what's the likely BC for an FMJ of that weight? With a BC in the 0.42-0.45 range, to match 7.62 M80 trajectory and drift, it'd be necessary to have MV in the neighborhood of 2700 fps, and that just ain't gonna happen.

Could be. We may be able to get away with being close enough to M80 performance for the difference not to be significant, rather than exactly matching it. However, if the long-range performance falls noticeably short then the new round won't be able to replace 7.62mm and the argument for it will thereby be substantially weakened IMO. That PKM is far too widely distributed in actually or potentially unfriendly hands for the troops to be expected to face it with weapons of inferior range.