1. Install the trigger mechanism in a manner
similar to the standard trigger mechanism, using the instructions provided with the
trigger mechanism.
2. Allow the trigger to break in with
approximately 500 rounds of live or dry firing. There should be a slight amount of
"creep" in the second stage. (If not, no tuning is needed.)
3. If tuning is needed, it is performed with
the trigger mechanism installed in the lower receiver; removal is not needed. The length
of trigger pull is divided into two regions: the first and the second stages. The second
stage is initiated when the top front of the disconnector contacts the rear of the top
hook of the hammer when the trigger is pulled. The added weight of trigger pull felt after
contact provides the second stage. Reducing the interference between the hammer and the
disconnector decreases the length of the second stage to the point that no creep is
detectable.
4. To reduce the length of the second stage,
place a 1/4 inch wide fine Arkansas stone on the hammer, contacting the top rear tip of
the hammer and the rear surface of the rear hammer hook. Stone the hammer hook VERY
slightly; only a thousandth or two. Check for second stage creep. Several repetitions may
be needed before any change is noticed. From this point only a few thousandths of cut is
needed. Assure that top and bottom edges of your cut across the rear surface of the hammer
hook are parallel. If they aren't, the cut is crooked. As soon as the second stage is
undetectable with a NORMAL trigger pull technique, stop cutting. No further tuning is
needed.
5. Took too much off? You know you’ve stoned
too much if there is no second stage or if the trigger catches on the microscopic radius
on the hammer hook and doesn’t return to the forward position when released. A slight
error can corrected by removing the trigger assembly from the receiver, removing the
disconnector, and stoning a thousandth or two from the front face of the disconnector.
Reinstall. Adjustments to the weight of the trigger pull may be made by reducing the
length of the disconnector spring with a belt sander. Repeated removal of the hammer from
the receiver can damage the hammer pin retaining spring inside the hammer or the pin holes
in the receiver.
6. Tuning the ArmaLite two stage trigger can be
accomplished in minutes by a skilled technician. Once tuned, the mechanism doesn't require
frequent maintenance: it is much less prone to problems than mechanisms equipped with a
screw which pivots the disconnector.
