Discharge side effect never fires

According to the helpfile it is supposed to do some kind of side effect periodically. I have used discharge hundreds of times and never seen any kind of side effect or echo or "increase in damage". Could the success rate for this, with HPM and/or without, be reviewed? Every other exotic affect does its side effect almost all the time. Project is also similar, and is very rare, but I have seen it, but never Discharge. Thanks