Bore Brush
Also: Bronze Brush
A bristled, caliber-sized brush that threads onto a cleaning rod to scrub carbon and copper loose from the rifling.
A bore brush is a twisted-wire core with radial bristles, sized so the bristles bear against the rifling as it passes through. Bronze brushes are the common workhorse because the soft phosphor-bronze bristles scrub hard caked deposits without scratching the steel, while nylon brushes are gentler and chemical-resistant for use with aggressive solvents. The brush mechanically breaks up stubborn residue that a patch alone will just glide over.
In practice the brush is soaked in bore-solvent and stroked through on a cleaning-rod to loosen baked-on carbon and to help lift copper-fouling that wet patches then carry out. Push it fully out the muzzle before reversing rather than changing direction mid-bore, which preserves the bristles and the crown. Once the heavy fouling is broken loose, clean patches finish the job.