Competition Bushing Neck Sizer Die is similar in concept to the Competition Seating Die, the cartridge case is completely supported and aligned with the sizing bushing before the sizing process begins. Bushings are purchased separately.
Neck wall thickness varies brass manufacturer to brass manufacturer. Depending on your situation, you will probably need a selection of bushings if you are loading different brands of brass. One way to measure for bushing size is to use a ball micrometer and measure several cases and then average the results. 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 number arrive at is used to determine your neck bushing size. Common wisdom suggests that you for every application you will neck a certain amount of neck tension.
For single loading in a bolt gun, optimum neck tension would be 0.001".
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".
For an example in the 308 Winchester the case mouth measurement came to 0.338" of a loaded round. So the bushings would be 0.337"/0.336"/0.335"
