Found this a Youtube. WA M4 with what looks to be a Mode2 Suppressor
http://www.gb-tech.com.tw/_newsite/images/images/head_01.gif
Um, looks more like a tracer unit.
+1 definately a tracer, you gan see the nice little green glow on the bb's
Damn it I see what you are talking about ...my bad.
http://www.gb-tech.com.tw/_newsite/images/images/head_01.gif