lysanderxiii
Member
Here is a graphic of the trajectory of M855 using various zero methods.
- The blue line with triangles is the trajectory when you put a target out at 300 meters and shoot at it until your point of aim and point of impact coincide.
- The yellow line with crosses is the trajectory if you set your M16A2 rear sight at 8/3 plus two clicks, put a target out at 25 meters and shoot at it until your point of aim and point of impact coincide.
- The green line with squares is the trajectory if you set your M16A2 rear sight at 8/3, put a target out at 36 yard (33 meters) and shoot at it until your point of aim and point of impact coincide.
- The red line with circles is the trajectory if you set your M16A2 rear sight at 8/3, put a target out at 25 meters and shoot at it until your point of aim and point of impact coincide.
As you can see the green line and the yellow line are pretty much and exact match.
In the M4 graphic the blue line is the trajectory when you put a target out at 300 meters and shoot at it until your point of aim and point of impact coincide.
The orange is if you follow the Army's zero procedure, as described in FM 3-22.9. The green line is the trajectory if you follow the 36 yard zero procedure as described in the USMC manual MCRP 3-01A.
It should be also noted that MCRP 3-01A has this to say about reduced rage zeroing:
"Zeroing is conducted at a range of 300 meters/yards. If a 300-meter/yard range is not available, a prezero sight setting can be established at a reduced range of 33 meters/36 yards. This does not constitute a BZO. The process at this short range allows the Marine to “get a group” on paper in preparation for firing at 300 meters/yards. When a Service rifle is zeroed for 300 meters/yards, the bullet crosses the line of sight twice. First, it crosses the line of sight at 33 meters/36 yards and then again farther down range at 300 meters/yards as it reenters the line of sight (see figs. 8-20 and 8-21)."
So, the fact that the 36 yard reduce range zero yields results that are 2 inches low is acceptable as this will be refined when shooting is done at 300 meters.
All calculations were done with JBM Ballistics' on-line trajectory calculator, using the following parameters:
M855 Ball:
Weight: 62 grains
BC: 0.151 (G7, from ARL data)
Velocity-
- M16A2: 3020 fps at 78 feet (from MIL-DTL-63989)
- M4: 2910 fps at muzzle (from Army Evaluation Center tests of M4)
Sight height-
- M16A2: 2.59 inch
- M4: 2.63 inch
Temperature: 70 degrees F
Pressure: 29.92 inHg
Humidity: 50%
And, one click elevation of an M16A2 rear sight know is equal to 3/8 inch at 25 Meter, per the Army's 25 meter zero target.
Raw data:
- The blue line with triangles is the trajectory when you put a target out at 300 meters and shoot at it until your point of aim and point of impact coincide.
- The yellow line with crosses is the trajectory if you set your M16A2 rear sight at 8/3 plus two clicks, put a target out at 25 meters and shoot at it until your point of aim and point of impact coincide.
- The green line with squares is the trajectory if you set your M16A2 rear sight at 8/3, put a target out at 36 yard (33 meters) and shoot at it until your point of aim and point of impact coincide.
- The red line with circles is the trajectory if you set your M16A2 rear sight at 8/3, put a target out at 25 meters and shoot at it until your point of aim and point of impact coincide.
As you can see the green line and the yellow line are pretty much and exact match.
In the M4 graphic the blue line is the trajectory when you put a target out at 300 meters and shoot at it until your point of aim and point of impact coincide.
The orange is if you follow the Army's zero procedure, as described in FM 3-22.9. The green line is the trajectory if you follow the 36 yard zero procedure as described in the USMC manual MCRP 3-01A.
It should be also noted that MCRP 3-01A has this to say about reduced rage zeroing:
"Zeroing is conducted at a range of 300 meters/yards. If a 300-meter/yard range is not available, a prezero sight setting can be established at a reduced range of 33 meters/36 yards. This does not constitute a BZO. The process at this short range allows the Marine to “get a group” on paper in preparation for firing at 300 meters/yards. When a Service rifle is zeroed for 300 meters/yards, the bullet crosses the line of sight twice. First, it crosses the line of sight at 33 meters/36 yards and then again farther down range at 300 meters/yards as it reenters the line of sight (see figs. 8-20 and 8-21)."
So, the fact that the 36 yard reduce range zero yields results that are 2 inches low is acceptable as this will be refined when shooting is done at 300 meters.
All calculations were done with JBM Ballistics' on-line trajectory calculator, using the following parameters:
M855 Ball:
Weight: 62 grains
BC: 0.151 (G7, from ARL data)
Velocity-
- M16A2: 3020 fps at 78 feet (from MIL-DTL-63989)
- M4: 2910 fps at muzzle (from Army Evaluation Center tests of M4)
Sight height-
- M16A2: 2.59 inch
- M4: 2.63 inch
Temperature: 70 degrees F
Pressure: 29.92 inHg
Humidity: 50%
And, one click elevation of an M16A2 rear sight know is equal to 3/8 inch at 25 Meter, per the Army's 25 meter zero target.
Raw data: