Lets start over: how do you design a GPC?

[stanc]

Green and that will meet the agreements we have made in the Geneva Convention will be a fundamental difficulty in accomplishing that design for sure...

The latter is no problemo. We have a JAG who has demonstrated he will approve virtually any bullet design the military wants to use. Examples:

- Sierra MatchKing hollow point bullet (7.62 M118LR, 5.56 Mk262)
- Barnes TSX expanding hunting bullet (5.56 "Optimized")
- ATK SOST expanding, fragmenting hollow point bullet (5.56 Mk318, 7.62 Mk319)

...but if we are to keep the M-16/M-4 lower...you have to have a long pill and a short fat case to make the long pill possible. No?

Depends on the bullet diameter. AR Performance developed a 6x41mm round using a slightly shortened SPC case that could be a potential candidate to upgrade 5.56 weapons.

Of course, there is no requirement to stick with the M16/M4 lower.