Operator's Manual
30
31
18.1 Sight Assembly
1. Rear Sight Assembly
The rear sight assembly is attached to the top of the feed tray
cover. It consists of a rear sight aperture mounted to the sight
leaf, an elevation knob, and a windage knob. See Figure 36.
The rear sight assembly is
adjusted by hand. The rear
sight elevation knob is
graduated for the FN M249S
™
firing 5.56 mm NATO 62 grain
M-855 or equivalent from 300
to 1000 meters.
2. Front Sight Assembly
The front sight assembly
consists of a protected front sight post mounted in an
adjustable front sight assembly attached to the gas block on
the barrel. When the FN M249S
™
is zeroed on the front sight
assembly, the zero stays on the barrel if/when spare barrels
are used. Optional tools are used to adjust the front sight
assembly.
18.2 Zeroing Procedures
Your sights are pre-set to a mechanical zero from the factory. With
the rear sights set at “3” for 300 meters, a field expedient zero can
be obtained at 25 meters. Once zeroed at 25 meters, you should
confirm and adjust your zero at 300 meters. With the rifle zeroed at
300 meters, the rear sight elevation adjustments are graduated in
100 meter increments from 300 to 1000 meters using NATO
Standard M-855 ball ammunition. In order to ensure your rifle is
zeroed for you and your ammunition, follow these instructions:
1. Before making any adjustments, make sure the slide hammer
is cocked and the safety selector is in the SAFE position as
explained in Sections 10 and 11, the rifle is cleared as
described in Section 17 and the muzzle is pointed in a safe
direction.
2. To mechanically zero your rifle’s sights for windage, you must
first center your rear sight aperture. Each sight may vary as to
how many clicks are needed to center the sight. To check your
sight, start with the sight leaf all the way to the left; counting
the clicks, rotate the windage knob (front knob) until the sight
leaf stops on the right side. See Figure 37.
Divide the number of clicks by two and move the leaf sight left
to center - Example: 24 clicks=12 to center; Example: 23
clicks = 12 to center (11+12=23, Use the larger number).
With the rear sight aperture mechanically centered, note its
location on the graduated windage scale on the rear of the
sight. Record its setting for future reference.
3. The rear sight aperture is adjustable independent of the
elevation knob for zeroing purposes. If you have only a single
barrel, it is recommended that the elevation be zeroed on the
rear sight aperture. Although it may be zeroed on the front
sight as explained in Step 6.
feed tray cover. See Figure
33. Leave the feed tray
cover open in the 45
o
or 90
o
position.
4. Pull the charging handle to
the rear to cock the slide
hammer. The safety selector
should now be placed in the
SAFE position as explained
in Section 10, if not already
done so.
5. Hold the charging handle to
the rear with the right hand
while lifting the feed tray
with the left hand to inspect
the chamber for the
presence of cartridges.
Remove any that remain.
See Figure 34.
6. Verify there are no loose cartridges in the magazine well.
7. Allow the charging handle to move forward, closing the bolt on
and empty chamber. Please note that the bolt will not
automatically lock in the rearward position. As a good safety
practice, hold the bolt open and visually inspect the chamber
to be absolutely certain a live cartridge is not present in the
chamber or anywhere in the rifle. The manual bolt lock device
may be used to manually “lock” or hold the bolt in
the open position as explained in Section 12.
8. Close the feed tray cover.
18. SIGHTS AND ZEROING
WARNING! BEFORE ADJUSTING THE SIGHTS, MAKE SURE THE
SLIDE HAMMER IS COCKED AND THE SAFETY SELECTOR IS
IN THE SAFE POSITION AS EXPLAINED IN SECTIONS 10 AND
11, THE RIFLE IS CLEARED AS DESCRIBED IN SECTION 17
AND THE MUZZLE IS POINTED IN A SAFE DIRECTION.
FAILURE TO FOLLOW THESE WARNINGS COULD RESULT IN
SERIOUS UINJURY OR DEATH.
Description of Sights
The FN M249S
™
rifle includes front and rear sights that are
adjustable for elevation and windage. It also includes an integral
MIL-STD-1913 pattern rail on the top of the feed tray cover.
See Figure 35.
FIGURE 33
FIGURE 36
FIGURE 35
FIGURE 34