The five bushings that come with the l-n-l headspace gauge provide the ability to check most bottleneck cases, from 17 Rem through the Belted magnums. Ackley improved chambers use the same Bushing size as the parent case. See chart provided or consult product instructions for cartridge/Bushing size details. Body with 5 Bushing set a.330 , b.350 , C.375 , D.400 , E.420.