Looks like True Velocity has delivered their ammo to Army

[stanc]

Trying to figure just how that’s done. Maybe hype... maybe using a special powder that prolongs its pressure curve over the typical one.

Maybe. Being bullpups, the GD guns have barrels 3-4 inches longer than the conventional configuration used by SIG, so could use a somewhat longer pressure curve.

Then there is also the matter that the PR statement is vague, and does not say what the chamber pressure is. The "safe operating pressures" could still be very high.