Page 129 - FAT 105 4.17 MOODLE

of the trigger must cock and release the ham- involve deactivating some type of trigger
mer/striker. The double-action system also has safety. Pre-travel is not part of every fire
the same benefits as the single-action trigger control group design.
when the hammer/striker is cocked. Another
• Creep – Creep is the feel of the sear sur-
benefit of some double-action trigger systems is
faces on the trigger/sear and hammer/
the ability to restrike the primer if the first at-
striker shearing across each other. A cer-
tempt fails. This is especially useful with semi-
tain amount of creep is a necessity for safe
automatic actions because simply pulling the
function, but an excessive amount of creep
trigger could resolve what would otherwise be
can be bad for accuracy and precision; too
a malfunction. The same benefits that make the
little creep and the system may fail to en-
system safe are also the same hindrances that
gage or reset, causing a misfire. Creep be-
make it a bad choice for accuracy. The long,
gins at the wall between the first and sec-
heavy pull allows for greater disruption in the
ond stages and ends at the “break.” Both
firearm before discharge, diminishing the ability
the trigger/sear and hammer/striker are
for precision.
sprung in such a way that they force the
SINGLE- AND TWO-STAGE sear surfaces into each other. Depending
TRIGGERS on how well the parts were machined and
finished, the sear surfaces may be mirror
Before talking about single- and two-stage trig- smooth, or rough, drastically affecting the
gers we need to discuss some of the terms in- feel of the creep.
volved in the feel of the trigger when it is pressed.
Understanding how each of the stages of the • Break – Break is the feel of the trigger/sear
releasing the hammer/striker. The shape
trigger press operates and feels will help you to
diagnose and remedy any issues that may arise of the edge of both sear surfaces and the
hardness of the parts will determine the
with the fire control group. The following terms
describe the different stages of the trigger press: feel of the break. With other designs the
tolerances of the parts involved will also
• Pre-Travel/Take-Up – Pre-travel or
affect the break. The feel of the break may
“take-up” is the slight movement of the
be one of two ways: crisp or soft. A crisp
trigger before reaching the “wall” or trig-
break will feel like a piece of glass break-
ger engagement. This initial movement
ing — sudden and sharp. A crisp break is
allows the trigger to engage the rest of the
from sear surfaces with sharp edges that
fire control group to begin the process of
are very hard. The sear surfaces will clear
releasing the hammer/striker. Often with
each other suddenly, creating a break that
the take-up, only the trigger and possibly
is a surprise. A soft break will feel like a
some linkage will move until the system
twig breaking. You will feel the sear sur-
engages the sear surfaces of the trigger/
faces roll off of each other and be able to
linkage or sear and hammer/striker. This
anticipate the break. A soft break is caused
engagement is known as the wall. Beyond
by sear surfaces with round edges or soft
the wall, the sear surfaces begin to shear
material being used for the trigger/sear
past one another before the hammer/
and hammer/striker. The sear surfaces will
striker is released. The pull weight of the
reach the edge and roll or slide past each
pre-travel is also very light compared to
other, making the break feel soft. With
the second stage. With some trigger de-
some striker-fired, semi-automatic pistol
signs, part of the pre-travel may also

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