This picture shows the first sign of headspace separation on two fired
.308 Winchester cases. Notice the bright horizontal ring
near the base of these cases. This is a common problem for
handloaders, when cases don't resized properly. Avoiding this
symptom often means going beyond just reading the instructions that
come with resizing dies. Headspace separation is caused when the
case shoulder gets pushed back a few thousandths of an inch too far
during the resizing operation. If you measure your cases (at the
shoulder), this can be avoided by setting your die height more
accurately.
If you ever experience this warning sign
of headspace separation take it seriously, and throw those cases away.
The next firing would definitely split these cases in two,
leaving most of the case stuck in your chamber. The escaping
gases can blow back through the bolt, and cause serious injuries.
If your chamber clearance (at the shoulder) is a bit too long,
your handloads might not chamber properly. If the case shoulder
gets pushed back too far, your handloads will be too short for your
chamber. When a short case is fired, its shoulder is blown
forward until it fills up the chamber. This stretches a case
just above the web (the solid part of your case). At this point
the case becomes paper thin, and it's wasted. These cases could
have been used for many more loadings if they had been accurately
measured at the shoulder during the reloading process.
Until now, hardloaders have used several different
methods of measuring chamber clearance. These methods include
coating a resized case with soot from a candle or using a Magic Marker,
and then chambering it to see where it contacts the chamber.
