Dillon Precision Products RL550C, Assembly And User Instructions Manual

Page: 69 / 76

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16.3 Head Space—Case Sizing
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Headspace is an important reloading parameter. Cartridge headspace is the distance from the case head to the part
of the case on which the cartridge stops moving forward in the chamber. Chamber headspace is the distance from
the breech face to the part of the chamber that stops the case from moving forward. Headspace in its common
usage (head clearance) is the difference between the chamber headspace length and the cartridge headspace length
or the amount of clearance front to back the cartridge has in the chamber. If the cartridge headspace length is too
long for the chamber, the bolt/slide will not close and the firearm will not go into battery. If the cartridge
headspace length is too short for the chamber (too much front-to-back clearance), the primer may not go off, you
may get poor accuracy, stretched brass, short brass life, flattened primers or case head separation.
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An example of stretched/failing brass is shown below. The brass “flows” towards the neck during the firing process
and can cause the case wall to get thinner in a “groove” on the inside culminating in a “halo” or crack on the
outside of the case as shown below:
Examples of “stretched brass” --impending case separation
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Cartridge types head space differently. Rimless auto pistol cases headspace on the mouth of the case. Rimmed
cases headspace on the rim. Bottleneck rimless cases headspace on a mid-point on the shoulder. Belted magnum
cases headspace on the belt (some will also headspace on the shoulder).
Lube Dents
“Halo”
indicating
impending
brass
separation
Brass
thinning from
the inside out