I think there should be a luck in the chamber type perk that suppresses supers.
"Super Suppressant" one random bullet in a magazine can suppress abilities (supers included)
The gun can either be a scout rifle or hand cannon and can be called the "Suppressor"
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It would have to be a special or even a heavy weapon, with very limited ammo, but guarantees suppression. How about a grenade launcher which fires suppressor explosives? It would have a smaller blast radius than the grenade, but similar damage.