A closer look at the Echo1 ST6 DEVGRU M4 RIS AEG that is right now available at Airsoft Master... "The Echo1 ST6 M4 is one of Echo1’s most popular M4 AEG. Here we will look at the features and specs of this AEG. From the front of the gun, the ST6 M4 comes with a plastic orange bird cage flash hider. The triangle front sight is adjustable for elevation, right under the triangle front sight is a sling mount. The metal outer barrel is 10in.