Bombarding Weapon Fusion
(from Starfinder Armory)
The bombarding fusion allows a weapon to duplicate the effect of a single grenade that is loaded into an extradimensional space within the weapon. Loading a grenade into a weapon with the bombarding fusion takes a full round, as does removing a previously loaded grenade. A grenade loaded into a weapon with the bombarding fusion cannot have an item level greater than the weapon’s item level. The grenade cannot be detonated, sundered, or otherwise affected while it is within this extradimensional space, and if the weapon is destroyed or gains the broken condition, the grenade is permanently destroyed.
Once per day, a weapon with the bombarding fusion can launch a mystic version of the loaded grenade. This acts as throwing the grenade, and uses the same proficiency and range increment as throwing a grenade, but does not require a free hand. As long as you are wielding a weapon with the bombarding fusion and it has not yet used this ability, you can launch the grenade as a ranged attack. Once this ability has been used, the loaded grenade can be removed from the extradimensional space, but a new grenade cannot be loaded into it until 24 hours have passed.