Probably this weapon can be a primary weapon, but as an assault rifle/SMG/Springfield Rifle with an attached grenade launcher.

Stats:

+ RMB fires a powerful nuke grenade that deals 450 base damage
+ Grenade has additional 15% blast radius
+ Grenade has additional 25% projectile speed

- Higher damage falloff within blast radius
- Only one grenade in clip. Can only be replenished in a resupply closet.
- Grenade will detonate once it hits a wall or the ground and will only deal 25% damage.

In short, this weapon is like loch-n-load + ullapool caber. It can take out a small cluster of enemies (2 or 3 enemies?), such as enemies pushing cart/ capping a point/ sentry nest. It has a larger blast radius but damage falls off much more as compared to the Grenade Launcher.

Counter to this weapon: Spread out so as to avoid becoming cluster targets

These are my suggestions, so any opinions?