The SX2 is a self adjustiong gas operated weapon. While I've little experience with the SX2 these types of weapons sometimes exhibit accelerated bolt speeds if the gas bypass becomes clogged by carbon or fouling. The accelerated bolt speed causes the bolt to open before the pressure has dropped completely in the barrel. This can escape as a flash from the ejection port. Also how much flash are you speaking of. A small amount of flash is not unknown..