One of my shooting buddies has a Bushmaster XM15-E2S that every now and then will light off two. We can't tell if it's the trigger and I myself don't have a lot of experience with this particular weapon. Clearly. it can't be used as it is. Does anyone know if this is a common issue with this particular model I field stripped is completely this past weekend and see no evidence of any worn parts or battered edges to any of the internal components. Should it just be looked over by someone more knowledgeable than myself as my gunsmithing skills are the high end of amateur at best. Thanks in advance.