Re: best way to find the bushing size for neck dies?
Last summer, I spent an hour on the phone with Patrick Ryan at Redding on this subject...
I had just gotten a .40XB-300WM, and picked a bushing that was 0.003" smaller than the loaded neck.
But the sized cases ware WAY under the bushing size (now that can't happen, can it??) How can a 0.338 bushing give a neck OD of 0.333?? So I figured that the bushing was mismarked... and took it out and measured it. 0.338". I put the bushing on the sized neck and it rattled [img]images/icons/frown.gif[/img] [img]images/icons/frown.gif[/img] That's a very badd thing!
Pat first said he hadn't heard it this, and asked for the neck size of the fired cases... and after an hour with Pat, we came to following conclusion.
It turns out that the recomendation for 0.002" under is based on cases that have been shot in tight neck chambers... the type most accuracy nuts use. In this situation, the neck only expands maybe 0.001" over... or may still be UNDER, and still be tight on the bullet, after firing.
But if you use a chamber that is the typical 0.005" to 0.010" over the loaded round (like most field rifles)... the neck expands to fill the chamber and is now quite larger.
When put through the bushing, the radius of the bushing (R=0.018"), causes the brass to first flow at a 45-ish degree direction to the center line... and when it gets to the bushing bore size, it overshoots several thou... thicker necks cause more overshoot.
So you can size a 308 cal case with a .338 bushing and wind up with a 0.330 OD neck [img]images/icons/frown.gif[/img] [img]images/icons/frown.gif[/img]
I doubt that there is a way to buy only one bushing... so except that several bushings just come with the territory [img]images/icons/frown.gif[/img]
[ 03-22-2003: Message edited by: CatShooter ]
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