Testing, testing...

[Tony Williams]

It seems to me that barrier defeat and wound trauma must be equal to 7.62mm, or both the troops and the decision makers will object to replacing 7.62x51 with a less effective round. If we were still talking about replacing 5.56x45 only, that would be a different matter.

I don't think so. The official view of both the US and UK armies (which is what we need to address, whether or not we think it is right) is that 5.56mm is adequate to around 400m; if all future engagements were to be within this range, 7.62mm would promptly be returned to support status. So the main focus of an intermediate round in replacing 7.62mm must be its long-range performance. From that perspective, improved penetration and effectiveness at short range (compared with 5.56mm) is a secondary advantage - although I believe a very important one.

I went back and reread what little info is available on the 7mm UIAC. It turns out that the 2650 fps published muzzle velocity is for a 16-inch barrel. (I was under the mistaken impression that it was for a 20-inch tube.) That translates to ~2750 fps out of a 20-inch barrel, with a lead-core, 130gr bullet.

Cris was also talking about a heavy, long-range sniper load of 175 grains at 2,400 fps. I'll have to ask him about this - I'll be seeing him next week.

I guess that brings up the question, is a 25% reduction in ammo weight "good enough" to make the switch worth the costs?

Two different scenarios: if LSAT proceeds, the same cost would be involved whatever calibre is chosen. If LSAT fails, there is still a chance of introducing a new calibre (although the likelihood drops sharply) through stressing the "combined advantages":

1. To reduce the weight compared with 7.62mm ammunition without losing long-range effectiveness.
2. To improve the effectiveness compared with 5.56mm ammunition without the heavy recoil of 7.62mm.
3. To provide greater tactical flexibility, with all riflemen being equipped with weapons effective at all combat ranges.
4. To save on procurement, support and training by halving the number of different small arms acquired.