RCBS Tungsten Coated Neck Sizing Bushing is designed for precise bullet tension without case lube, due to its Tungsten Disulfide coating.
It should be used exclusively with RCBS Gold Medal Match neck sizing dies, and works best with high-quality brass of consistent neck thickness.
To select the correct bushing size, subtract .002"-.003" from the loaded cartridge's outside neck diameter or calculate based on neck wall thickness and bullet diameter.