Testing, testing...

[JASmith]

...From .50-70 to 45-70 to .30-40 to 30-03 to 30-06 to 7.62x51, the Army made only "5%" improvements. (5.56x45 was forced upon them by the SecDef, so it's an anomaly in the historical trend.)

I'm sure that Gene's 50% is more rhetorical than not. The facts are, however, that we will gain exactly zero traction if we are able to demonstrate only a 5% improvement absent a political decision to go to a new cartridge.

Also, the move from each of the cartridges to the next in the list had more than 5% improvements in one or more metrics. For example, the .45-70 had a slight improvement in velocity for a significantly smaller case. The .30-40 Krag had, IIRC a 220 grain bullet replacing the 400 grain+ 45-70 bullet and a lot more cartridges, and so on.

So yes, the improvement in some metrics in each of these may have been flat or a slight improvement, there were almost always significant improvements in one or more metrics. The exception may have been the 7.62X51 -- I don't know for sure but aside from the political issues (always trumping technical), the improvement was in weight of brass and a mild reduction in recoil at the expense of a slight reduction in velocity. The political issue was imposing a common cartridge on NATO and getting everyone to go with our beloved 30-06 would not have worked.

SecDef imposed the 5.56 DoD-wide because his metrics told him there was much more than 50% — doubling (100% improvement) the numbers of rounds per pound. This overrode issues like terminal effects simply because the 5.56 was viewed as adequate for the muzzle out to the 200 or so meter fight. For that matter, it still is.