Figure 14-16.--Aligned sight picture.
Figure 14-17.--Compensated sight picture.
the ALIGNED sight picture (fig. 14-16). If the two
aiming posts do not appear as one, displacement of the
direction center (FDC) to know whether or not a
sight or the baseplate has occurred. This separation is
particular mission can be completed with that mortar.
caused by one or two things: either (1) a large deflection
shift that moves the entire sight out of the plane passing
To determine mask clearance, the gunner sets the
through the aiming posts; or (2) a lateral (left or right)
sight at 0 deflection and 0 elevation, making the line of
displacement of the baseplate caused by the shock of
sight parallel with the axis of the bore. The gunner then
firing, which also moves the sight out of the plane of the
raises or lowers the barrel until the cross hairs of the
aiming post. When both the far post and the near post
sight just touch the obstruction (tree, hill, etc.). The
are visible, it is called a COMPENSATED sight picture
gunner then levels the elevation bubble by turning the
elevation knob on the sight and reads the elevation from
the elevation scale. This reading is the minimum (or
maximum, depending on the location of the obstruction)
mask clearance. For a safety factor, 30 mils is added to
Mask clearance is the clearance required for firing
(or subtracted from) the elevation reading.
the weapon without danger of a premature detonation of
Mask clearance must be determined in a complete
the round by obstructions, such as trees, hills, or
circle around the mortar to every object that could
buildings. After the mortar is mounted, the gunner must
interfere with firing. The gunner reports all these
determine the minimum and the maximum mask
figures, stating the azimuth and clearance to the squad
clearance. This determination helps to ensure troop
safety at the mortar position and also helps the fire
leader and FDC. He also keeps a record for himself.