Most Synedrion ammo magazines are actually power cells for their energy weapons. If, like in WH40k where Imperial Guardsmen could use their Lasgun cells as improvised grenades in a pinch, Synedrion soldiers could throw their own ammo clips as a grenade as well. The increased cost of Synedrion clips vs. others roughly matches with that of actual grenades already, and they take up the same amount of inventory space.
Balancing this would revolve around the fact that ammo can be produced instantly, while grenades take time. Also in how you would need a reason to take regular explosive grenades vs. just bringing Synedrion ammo clips; perhaps you can only use the clips as grenades if you have a Synedrion weapon of that clip type? Also, the damage of the blast would be proportional to the ammo left in the clip.