Be creative here there are no wrong ideas.
I would like the Spartan laser to be a weapon personally, just called something different "Charge Rifle" was a name I had in mind
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Maybe some kind of pulse fire/double shot/semi auto hand cannon. Melee special weapons - perhaps using ammo as a sort of energy based timer when activated? Hold ADS to activate (consumes ammo) then fire to attack? Maybe this same type of thing as an activatable energy shield? Hellfire type rockets? Less damage and blast radius but multiple rockets fired per shot