Out of pistol ammo? That would be a problem if you don't have the original shotgun from Halo Combat Evolved.
If you do have it, well, everything is fine. Every living thing within five meters will be dead momentarily.
The original Halo's shotgun could and would kill to a ludicrous distance, had plenty of ammo, and employed just the right amount of speed to its reload. Even better, it had style, gave off a chunky sound when fired, and allowed for a quick melee follow up if anything was still moving after eating a load of buckshot.
Other games might have had better aesthetics for their shotguns, but nothing beats death by a thousand pellets.