Think it is strange that there are no grenade launchers in fallout 3 and 4, mostly 4 with the heavy customization options.
I mean think about it, grenade launchers would be an epic class of weapons, weaker then rockets but more common ammo and different functions. like a incendiary launcher that creates a pool of fire on impact. also grenade launchers would be a cool weapon if you use the explosives perk.
for this I have a suggestion (highly unlikely that the devs read this), add 3 types of grenade launchers.
type one: grenade rifle
info: based on the m79 has 4 upgrade slots, base damage 100
slots: stock, grenade, barrel, sight
stock upgrades
short stock: base
full stock: increase accuracy, lower recoil
padded full stock: superior accuracy, superior recoil control.
barrel upgrades
single barrel: base
pump barrel: triples ammo count pump to fire, slower reload.
long single barrel: longer range
long pump barrel: triples ammo count, pump to fire, slow reload, longer range.
sight upgrades
none: base
range sight: adds a range marker to hud (basicly the bar lines seen on most GL huds)
tech sight: when aiming, shows range (top right), projected arc, and distance to target.
grenades
note: all grenades are the same 40mm ammo
explosive: base
high explosive: superior damage, inferior range.
fragmentation: superior splash, lower damage
gas grenade: enemies in target area may drop weapon and cover eyes and mouth (gasmask or raider masks negate)
incendiary: inferior damage, 50% chance to light targets on fire, target area lit on fire for 10 seconds dealing minor damage(2 per second).
flash bang: stuns enemies hit, for 3 to 5 seconds does low damge
flare: uses flares instead of 40mm, if fired into the air summons minute men.
type two: Grenade revolver
info: based on the m32 milkor grenade launcher, has a higher rate of fire but a lower reload. other then that has about the same stats.
upgrade slots: stock, tube, barrel, sight, grenade.
stock upgrades: same as the grenade rifle.
grenade: same as grenade rifle.
tube upgrades
4 round tube: fast reload, lower ammo count. (default)
6 round tube: slow reload, moderate ammo
10 round tube: slowest reload, highest ammo cap.
barrel
short barrel: default
suppressed barrel: will not alert enemies when fired. (the explosion will still alert them but they will not see where it came from)
long barrel: superior range
sights
line sight: default shows range lines.
tech sight: grenade rifle
tracking sight: when zoomed shows green triangles for all "targets" shows red for all that will be hit, predicts movement with 95% accuracy
type three: the unslung grenade launcher
info: this is a barrel mod for the combat rifle (The .45 one) or shotgun that removes the thrown grenade ability and replaces with a launcher that must be reloaded after use, the advantage is more range and more damage, but at a cost of being able to spam grenades. (holding grenade button will swap to it, giving the arc if perks are had and reloading if needed hold again to swap back)
looks: m203 combined with a gp-30
upgrades: as the unslung is an upgrade it only has one that it adds ot the weapons, the grenade types which are the same as the grenade rifle.