Proper Neck Sizing Bushing

[billmo]

In an article written by Mr. Jacob Gottfredson called Prep. Cases for Long Range Accuracy,step # 9) he gave a method for selecting the proper neck sizing bushings for turned neck brass. Should that same method be used for "no turn" brass as well?
Thanks, Bill

 

[tenring]

If you know your chamber neck diameter, you should also know that loaded round at neck should be about .001 - .002 under that dimension. Try bushings that are 1 - 2 thou less than the loaded diameter. For instance: Chamber neck is .262; loaded round should be .260 - .261; bushing could be .258 - 259.

 

[Hipshot]

For "proper" neck tension, measure a loaded round at the neck, then subtract .002 to .004 to get the bushing size. Minus .002 for naked bullets and minus .003 or .004 for moly or other coated bullets. It does not matter if the cases are neck turned or not.

If your chamber is cut small then you probably will have to turn case necks. The chamber neck diameter has to be somewhat larger than the seated round neck diameter so that the case neck can open up to release the bullet; how much larger the chamber diameter needs to be is a much discussed subject. I think most go for .002 larger. Another rule of thumb is that if you take a fired cartridge case and slip a bullet, nose first into it, the bullet should slip through with just a hint of wobble, or, little to no friction. If the case neck does not open enough for the bullet to be released easily then bad things will happen.

The other side of the coin is that if the chamber too large for the cartridge then upon firing the nect opens "too wide" as hurts the accuracy of the bullet entering the barrel.

Oh, what fun we have working these things out