The Metalstorm 3GL is an electronically fired 3 Round (!!!) 40mm low pressure grenade launcher. The rounds are stacked in a single unit at reloading, and can then be fired front to back in quick succession.
Arma 3 3GL's are single shot weapons just like the Opfor EGLM. This needs to be adressed: no point in using 3GL's when not making them live up to their name.
Source 1: Video demonstrating 3GL prototype on M16 (In AddInf below)
Source 2: Wikipedia article detailing the Metalstorm systems
Pick any MX-M GL equipped with a 3GL launcher and fire: one shot and reload!
As stated above, this is incorrect.
Source 1: http://www.youtube.com/watch?v=IP_GTx4o134
Source 2: http://en.wikipedia.org/wiki/Metal_Storm (Note: Bad article, however some information is relevant and concurrent with video evidence as shown above. However, take information with a grain of salt.)
Sorry, wasn´t supposed to be a "major" issue. :I Accidentially put in the wrong option in the drop down menu.
I apologize
With scripts you can add a few more ammo types that are only 'secretly' available in the alpha, and one of the ammo types I found is a working 3-round grenade magazine thing for the 3GL.
I actually thought it was broken until I read your explanation of it. XD
Wow that's pretty dissapointing that the 3GL is not working as it does in the real world. Although I can understand why the choice was made for that. OP weapon is kind of OP, 'specially in the AI's hands where their grenade launchers are deadlier than the rifles themselves.
For the sake of realism I think it would be a good idea to put 3 shots in the launcher as per reality.
I should´ve paid attention, the 3 round magazine for the 3GL is ingame.
It would be good to at least have the grenadiers use these, instead of single grenades, as a suggestion.