These barrels will fit both the RM4 AEG3s and the VM4 AEG2.5 Series rifles, including the original PTS Scout and CQB ERGs. You can select your desired length from the dropdown menu, but note that the Scout length barrel does not use a standard carbine-length rail system, but instead uses a mid-length rail system. For installation with a freefloat rail system, either outer barrel will fit! Part 370 is the stock outer rear barrel for the standard VM4A1, RM4A1, and the original PTS ERG RM4 CQB. Part 409 is the stock rear outer barrel for the original PTS Scout ERG, but will fit any VM4 or RM4 system.
Part 370: approx 9 inches from flange, including threading.
Part 409: approx 11 inches from flange, including threading