Overall, Soldiers like the new M320 40mm Grenade Launcher but prefer to carry it in the stand alone configuration due to its weight and attached aiming device. Employing the weapon in this fashion also has the added bonus that the Grenadier will concentrate on using the launcher as a primary weapon rather than an add-on the M16/M4.
The issue with this is how to carry it. Soldiers have dreamed up several Rube Goldberg contraptions to secure the weapon when not in use. However, the best answer I have seen is the Grenade Launcher Holster from S&S Precision. Available in left and right versions, the mounting systems allows the holster to be attached to the armor at virtually any angle. Since most troops use the launcher with butt stock, there is also a paddle available for the holster to allow it to be hip mounted.
The launcher is held in place by a molded plastic shroud that grips the barrel. Additionally, the barrel sits atop a plug that features an O ring designed to keep debris out of the muzzle. The Grenade Launcher Holster also comes with a bungee to further secure the weapon when needed.
I highly recommend that Grenadiers take a look at this solution. It is also something that the folks at PM-Individual Weapons should consider. Interested parties should email S&S Precision.