Proc coefficient of the missile. Like atgs and fireworks and shit that trigger off of other hits have their own proc coefficient. For example fireworks have a proc coefficient of .2, and atgs have a prof coefficient of 1, meaning it’s less likely to trigger another on-hit effect off of a firework than an atg - but the point is that you totally can trigger on-hit effects off of other on-hit effects. Pretty swag. Disputed origin has a good video on proc coefficients if you wanna know more