I am not sure you do: What I am saying is that there is no upside to switching from the 5.56x45 carbine the troops have now to, at considerable expense, a carbine chambered in a weaker cartridge. The current round (5.56x45) is lighter (basic load considerations), the case is smaller in diameter (magazine capacity issues) and it is much more powerful and has much greater range than a carbine chambered in .357SIG. The 7.62x25 is lighter and smaller than the SIG round, but it is still underpowered and as heavy as the current round. Where is the benefit to this?
The only complaints against the current round are that it is not powerful enough, and it lacks range for many of the actions in Afghanistan ...... picking a weaker round, without any benefit is ....... silly.
TheGolden Rule of Tool Use: "If you don't know what you are doing, DON'T."