Forster Neck Bushings
These neck size bushings are specifically for the Forster Bushing Bump Neck Sizing Die
If you’re making cartridges for a tight chambered rifle, you might need smaller bushings. Alternatively, you might need larger bushings if you are not outside neck turning and are using brass cases with thick neck walls. Most sizes are available in .001″ increments; just order by the inside diameter desired.
You can adjust the bushing height within the die to allow partial case neck sizing, allowing the unsized section to better align the cartridge in the rifle chamber.
What size do I need to choose? This depends. Brass neck wall thickness and the variation of thickness around the neck..
First measure if you can across the neck area after a bullet is seated in an average case you are using. Measure at 3 points around the neck and average the measurement. Once you have that measurement you will need a neck bushing size which is between -0.001″ (one thou) to -0.003″ (3 thou) less than you measurement just made.
-0.003″ for tight bullet seating tension. -0.001″ for light seating and in the middle for most.
For more information click here Forster Bushing Bump Neck Sizing Die Instructions