Forster Neck Bushings
These neck size bushings are specifically for the Forster Bushing Bump Neck Sizing Dies and the new Forster Full Length/neck bushing dies.
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 on 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.
Method 2: Using a proper wall thickness or tubing micrometer ( NOT CALIPERS) properly measure the wall thickness of the necks. Take several measurements around the case as they will vary. Average the wall thickness and write down the number. Then calculate: Your bullet diameter + wall thickness + wall thickness (because on a loaded round the wall thickness on each side).
Once you have that measurement, which should be the same result as above description, then take of 0.002″ from that measurement and that will be your bushing size. But consider one smaller or larger also as required.
Example: 0.3080″ + 0.0145 +0.0145″ = 0.3360″ and this would mean something around a “334” bush would be good.
For those reloaders using the new Forster Full Length/neck bushing die, they will notice that the decapping rod has an expander ball fitted. This ball can be removed if required for those who have outside neck turned barss.
But, for those who are NOT outside neck turning their brass, this expander ball is designed to stretch out the insides again after the sizing of the neck part and uniform the inside size. Therefore it is often useful to choose a neck bushing, one size smaller than the above calculation when in use with the expander ball in place.
NB: The bushing bump/neck die does not contain and expander on its decapping rod.
For more information click here Forster Bushing Bump Neck Sizing Die Instructions