Lets start over: how do you design a GPC?

[stanc]

The problem I see is the military doesn't know what they want. Someone will have to prove their system and then sell the idea to the military that it IS the system they need.
Everyone at the top is going to want what THEY think they need and they will cast a shadow of doubt on every product that they as individuals don't want.

That pretty well sums it up. The fact is, there have been a multitude of new cartridges developed over the years, many within the military itself. Only rarely does a new round get adopted. (Logically, they can't all be adopted, or the system would be in chaos.)

IMO, to get a GPC into service will require the active support of one or more high level entities, such as 5.56x45 and the AR15 received from the Commanding General of CONARC and others, in the late 1950s and early 1960s. Without such backing, the GPC will go nowhere.