The sights of the M240G are rugged and reliable. When setting battlesight zero (BZO), all adjustments (windage and elevation) are made to the front sight assembly. The advantage of this system is that it al- lows each spare barrel to be individually zeroed to the machine gun and then locked down with the ad- justment tools. This avoids accidental loss of zero through inadvertent manipulation during cleaning or inspections. BZO is normally established at 12.7 meters in preparation for qualification firing as de- scribed in this reference (see paragraph 31104). The upper row of aiming points (A-D) on the qualifica- tion target is designed for this purpose (see figure 3-71). However, any point of aim–point of impact type of target can be used as a field expedient, (e.g., the M16A2 BZO target).
The combination front sight adjusting tool is used for elevation and windage adjustments (see figure 3-72). This tool unlocks the front sight blade retain- ing strap and has a special slotted end piece to turn the front sight blade for elevation changes. In addi- tion, a hex wrench is included on another section of the tool. This hex wrench is designed to turn the socket head windage adjustment screws; however, it should not be used for this unless it fits the socket heads of the windage screws tightly.
a. Adjusting for Elevation BZO. For the initial firing groups, do not unlock or change the elevation setting of the front sight post. Begin with the front sight post set at the position in which it is delivered. Set the rear sight elevation at 500 meters. With a target at 12.7 meters, first correctly align the sights (see figure 3-73), then hold a tight/well-supported point of aim, point of impact sight picture (see
figure 3-74) and fire three rounds, one round at a time, taking time to realign the sight picture between shots.
If the shot group is above or below the aim point, the front sight needs adjustment. The combination tool is used to unlock the front sight retaining strap (see figure 3-75). Unlock the retaining strap and ro- tate it upward. The front sight post is now free to rotate. Apply two to three drops of lubricant (CLP, LSA, or LSA-T) around the base of the front sight to lubricate the threaded shaft of the front sight post. This will make it easier to rotate.
NOTE
The following sight adjustments are given from the gunner's perspective at the rear of the machine gun with the individual in a normal firing position or po- sitioned above the gun.
If the shot group is above the aim point, rotate the sight post counterclockwise as if it were being un- screwed. If the group is below the aim point, rotate the sight post clockwise as if it were being screwed in or down.
NOTE
Rotating the front sight post counterclockwise brings the point of impact down on the target, while rotat- ing the front sight post clockwise brings the point of impact up on the target.
At a range of 12.7 meters, one half turn of the post blade, will move the strike of the bullet by approxi- mately 1/5 of an inch (5mm). One full turn of the post blade will move the strike of the bullet by ap- proximately 3/8 of an inch (10mm). After rotating the post blade the required amount, lower the retain- ing strap, but do not lock it down until the BZO ele- vation is confirmed. Continue the above procedure until the elevation BZO is confirmed. If the post blade is required to be rotated counterclockwise to a point where its base is more than half way out of the assembly, it should be replaced with a Number 2 front sight blade which is taller than the Number 1 or normal sight. Once BZO elevation is confirmed, lock the retaining strap down to its detent.
b. Adjusting for Windage BZO CAUTION
The windage adjustment screws will break with the slightest over torquing. Be careful not to over tighten the adjustment screws.
As above, fire a group(s) to determine if a windage adjustment is required. If the group is to the left of the point of aim, the front sight protector assembly must be moved to the left to shift the point of impact to the right (towards the point of aim). If the group is to the right of the point of aim, the front sight protector must be moved to the right to shift the point of impact to the left (towards the point of aim).
NOTE
Moving the front sight post to the right moves the strike of the projectile to the left on the target. Mov- ing the front sight post to the left moves the strike of the projectile to the right on the target.
To move the group to the left, use a tight fitting hex wrench to loosen (turn counterclockwise) the adjust- ing screw on the right side of the front sight assem- bly the desired amount. Then tighten (turn clockwise) the opposite side screw (the one on the left side) exactly the same amount. At a range of 12.7 meters, one complete rotation (360 degrees) of the adjusting screws will move the point of impact approximately 1/3 inch (8mm). As the adjusting screws are turned, noticeable clicks (eight per revo- lution) should be detected. If this is not the case, an armorer should replace the protector assembly or the detente spring.
To move the group to the right, loosen (turn counter- clockwise) the adjusting screw on the left side of the front sight assembly the desired amount. Then tighten (turn clockwise) the opposite side screw (the one on the right side) exactly the same amount. At a range of 12.7 meters, complete rota- tion (360 degrees) of the adjusting screws will move the point of impact approximately 1/3 inch (8mm).
NOTE
The front sight windage adjustment procedure is the combination of creating slack on one side, and then taking up that slack from the opposite side. There- fore, the front sight protector assembly should al- ways be clamped tight between the heads of the two opposing screws. Each time one screw is loosened,
the opposite one must be tightened exactly the same amount.
Once the shot group is confirmed to be centered, check for play in the front sight assembly by lightly clamping between finger and thumb and attempting to move the sight assembly laterally. If there is no play evident, the windage adjustment is completed. If play is evident, carefully check both screws for looseness.
The 12.7-meter qualification course is fired with the BZO established as above with the rear sight set for 500 meters. Since the BZO procedure above cali- brates the rear sight for all targets within the effec- tive range of the machine gun, the estimated range to any other target should be placed on the rear sight and a good sight picture obtained before firing. If confirmation of the BZO is desired, this is easily done from the 200- or 300-meter line at a rifle range to disk the target shot group once it is fired. When firing, set the range on the rear sight and mount the weapon on the tripod or use a good field firing posi- tion with the bipod. If the dispersion of the shot group is too large to calculate the mean center of impact, load and fire one ball round at a time. Note that wearing a flak jacket or gas mask by the gunner may change the mean point of impact.
If firing confirmation zero on a range laid out in yards, do not be overly concerned if the point of im- pact is slightly above the point of aim, as the beaten zone of a normal burst will cover most targets. If a large number of very distant targets is to be at- tacked, using ranges estimated in meters taken from a map or range finder, add yards to meters elevation change to the front sight in, or clockwise, one-half turn. This is especially true if shot groups are just slightly low on a target at 200 or 300 yards. If this is the case always add the one-half turn yards to me- ters elevation change.
At 200 meters, one-half turn of the front sight blade, in either direction, moves the point of impact up or down approximately 4 1/4 inches (108mm). At 200 meters, one-half turn (four clicks) of the windage
screws will move the point of impact left or right approximately 3 1/8 inches (80mm).