I don't think the trigger is really dual stage as on the AUG. The AUG doesn't have a fire selector and relies on the 2-stage trigger for semi and full auto. The P/E90 has a fire selector. But lightly depressing the trigger on full auto did set off only a single shot, whereas squeezing it all the way went full-auto. I could do this on the TM P90 I tried as well so don't think it's specific to the Echo 1.