Burst Projectile Abilities - SmArtKar/AthenaFramework GitHub Wiki
Vanilla projectile launch comp doesn't support burst shots, but you could use Athena's CompProperties_AbilityLaunchProjectileBurst for that. It works similarly to vanilla's CompProperties_AbilityLaunchProjectile but you can specify the amount of shots and delay between them.
public class CompProperties_AbilityLaunchProjectileBurst : CompProperties_AbilityEffect
{
public ThingDef projectileDef;
public int burstCount = 1;
public int ticksBetweenShots = 5;
public SoundDef firingSound;
}