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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Haven't seen a double-barrel sawed-off shotgun yet; I'm picturing an exotic secondary that has virtually no range, but has extremely high rate of fire (simulating firing both barrels at once), fast reload, and does one-shot kills within its range. Not really a "new" type, but a variation of an existing.