The present disclosure provides, in part, new muzzle brakes, kits, and weapons systems (e.g., rifles) that allow for incremental adjustment of the ports of a muzzle brake so that the muzzle brake can be tuned for the user and firearm system. In certain aspects, the present disclosure provides muzzle brake plugs having an interior surface defining a plug bore that extends at least partially through the thickness of the muzzle brake plug and muzzle brakes having a plurality of side ports extending laterally away from a central bore and arranged to replaceably receive muzzle brake plugs. A bottom wall closing the plug bore of a muzzle brake plug can be selectively drilled or punch-out to create or enlarge an opening with the plug bore, thus allowing a shooter to tune the muzzle brake to the firearm system.