It's all depends on how thick the case mouths are. If the thickness is .015", you multiply that by 2 . . . = .030".
Take that outside measurement of .338" - .030" = .308" which is the size of the bullet and means the neck wall thickness is at .015". If you want the "neck tension" to be .002", the neck needs to be the size of the bullet less that .002 . . . or .306. The size of the bushing should be .3055 to allow for some springback of ~.0005". But, keep in mind this is based on a case neck wall thickness of .015". The bushing size changes for that .0020" "neck tension" with a different neck wall thickness.