The Redding Type S Bushing Full Length Size Die allows the reloader to precisely control case neck dimension and tension while sizing the body and moving the shoulder back. Type S Bushing Full Length Size Die use interchangeable sizing bushings that are available in .001" increments. Neck wall thickness varies brass manufacturer to brass manufacturer. Depending on your application, you will probably need a selection of bushings if you are loading different brands of brass. One way to measure bushing size is to use a ball micrometer and measure several cartridge case neck walls, and then average the measurements. To that average you double it and then add the bullet caliber. Another way to find the correct bushing size is to measure several loaded rounds, and then you average the readings. The calculated number arrived at is used to determine your neck bushing size. Common wisdom suggests that you will need a certain amount of neck tension for each rifle.
For single loading in a bolt gun, optimum neck tension would be 0.001” so you will subtract that from your average measurement.
For loading from bolt gun from the magazine, optimum neck tension would be 0.002”.
For loading from auto-loading gun from the magazine, optimum neck tension would be 0.003”.
An example of the 308 Winchester measurement came to 0.338”. So, the bushings would be 0.337” / 0.336” / 0.335”.
