From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: idea: neck sizer
Organization: Lawrence Berkeley Laboratory, California

Neck sizing of rifle cases is often helpful when accuracy is the goal.
This is because an unresized case locates itself well in the chamber
and helps center the bullet before launch.  If the neck of the case
is not completely homogenous due to different histories for different
parts of the case, the sized section of the neck may be forced off center
by neck sizing.  It is certainly desirable to use a neck turner for
consistent neck wall thickness, but even then, the sized section of the
neck may not be coaxial with the unsized portion.

One way to get the resized portion of a neck-sized case to be coaxial
with the unresized section should be to have a guide section in the
resizer which is exactly the same inside diameter as the neck of the
chamber.  After a case has been fired a number of times, it springs
back from the walls of the chamber very little; it becomes closer and
closer fitting to the chamber.  This tells us that the diameter of the
guide section of the die should be the same as the diameter of the chamber
neck.

Here is a sketch of a cross section of the proposed neck sizer:


                        |   |  <---  straightness maintainer
                        |   |
                       /     \ <---  active bevel
                       |     |
                       |     | <---  guide section
                      /       \
                     /         \ <-- feed bevel

The feed bevel just directs the case mouth up into the guide section.
The guide section forces the half of the case neck which is to be sized
to stay on center with the guided unsized section while the sizing takes
place.  The rest of the die keeps the sized section of the neck from
wandering - it maintains cylindricity and "coaxiality".

A few things to think about: If the neck wall thickness is uneven, the
off-centeredness of the bullet is guaranteed.  If you have a crooked
chamber, this sizer won't help.  If the case's base is not held
concentric with the sizer section, the sizing may be crooked.
Long-necked cases should work best: then the half of the neck which
remains unsized will give immediate guidance to the half which is
resized, and the half which is resized will be long enough to properly
grip the bullet.

I think the best embodiment of this idea might be a tube with an ID
equal to the OD of the fired case (plus .001 clearance) and a separate
sizer section as drawn above which is a slip fit in this same tube.
In use, one would slip the tube over the fired case and then push
the sizer into the tube and over the case neck thereby maintaining
concentricity.  Removing the sizer from the neck would be more
interesting but not too difficult.

John Bercovitz     (JHBercovitz@lbl.gov)

From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: idea: neck sizer
Organization: Lawrence Berkeley Laboratory, California

In article <49784@mimsy.umd.edu> toby@milton.u.washington.edu
(Toby Bradshaw) writes:

##                        |   |  <---  straightness maintainer
##                        |   |
##                       /     \ <---  active bevel
##                       |     |
##                       |     | <---  guide section
##                      /       \
##                     /         \ <-- feed bevel
##

#Neil Jones Custom Products has beat you to the punch with neck dies and
#seater dies with guide bushings.  His address, from Precision Shooting, is
#RD1, Box 483-A, Saegertown, PA 16433  (814)763-2769.

That's great!  Anyone know if he sizes the guide section to your chamber
neck?  Is the guide section integral with the active bevel or is it a
sleeve?  Anyone tried this die?  How well does it work?  What's the tariff?

Thanks,
John B