Wookieepedia reference on concussion grenades. I personally think the first is what it should have.
'Physical, Sonic
The first one was a fairly standard grenade, used by many factions. It exploded with a small blast radius, killing most organics and damaging equipment. A sonic shockwave was expelled in the explosion that stunned anyone right outside the 4 meter blast radius.
[edit] Sonic
The second kind did not detonate in a traditional sense. The common blast radius was 4 meters, fairly large for a handheld explosive. It created only the sonic shockwave, stunning anybody hit by it rather than killing or wounding them.
[edit] Physical
The third kind, designed for use against vehicles and equipment. The grenade was very useful against vehicles that where fast or slow moving vehicles because of its tendency to stick to vehicles armor. The grenade was not used much against organics, due to its small blast radius. '
What's more we should get its other armaments right too. Right now they have an all but useless dual cannon and that's it. It should have, canonically, a heavy double blaster which fires 2 shots in succession with a small area of effect, and a single E-WEB cannon for short bursts of anti-infantry fire. The heavies should fire a blast which is effective against infantry and light vehicles but with a large recharge time, only 2 per volley and inaccurate against infantry, relying on the explosion. The E-WEB should be a burst fire of anti-infantry used only when employed against infantry.
As with my EPs infantry have been modified to die more realistically (but not like flies) and are far bigger investments, there are also far more of them, so this shouldn't upset it too much, as with the infantry rebalances I have planned for vehicle beefing to be more properly to relativism.