No blueprint to learn, so read this as a price tag: some high quality metal and three pipes sit in every launcher you loot, and its rounds are loot too.
The launcher cannot be crafted or researched, so the Level 3 recipe on this page never becomes yours. Every one you own came off a heavy scientist or out of an event bag, as the item page says. Read the bill as what the gun is worth in parts: a little less metal and one pipe fewer than a rocket launcher.
What decides keep or scrap is the ammo, not the gun. All three 40mm rounds are loot as well, from the cheap 40mm shotgun round to the HE grenade with an explosive inside. A launcher with a stack of HE is worth holding for the night your base gets raided online. A launcher with nothing to load is just metal and pipes in a box.
Tip
Then recycle it, but know the rate. The ordinary recycler returns about half the metal and a metal pipe, sometimes two. Better than letting it rot, and far short of the bill above.
Questions
Multiple Grenade Launcher ×10: how many resources?
High Quality Metal ×250, Metal Pipe ×30.
Which workbench does Multiple Grenade Launcher need?
Workbench level 3.
How long does Multiple Grenade Launcher take to craft?
