Failure2Stop
07-04-09, 14:22
*This is in respons to a question in another thread (https://www.m4carbine.net/showthread.php?t=33717) that I thought would be a bit of a hijack if I replied in that thread, so I started a new thread.*
I have done a bit of shooting from weird positions to see what I can get out of them. To try to get solid info I did it with 1X optics and irons as well as with a 4X ACOG. There is a little bit of difference between the two categories, but mostly due to zero distance than magnification.
Here's how I explain it to guys that go through my courses-
When your rifle is in it's "normal" orientation the bullet travels upward at a determined angle to meet your line of sight at the initial point, continues up until it reaches the culminating point, and drops to meet the line of sight again at the true zero range (since we zero at the second cross-over with most optics to ensure maximum efficiency).
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory1.jpg
However, when we turn the gun sideways (let's take the urban/roll-over prone for the example since it is at or very close to a 90 degree offset), the bullet's trajectory will never cross-over the horizontal plane of the sight other than as it leaves the muzzle.
Why?
Beacuse when the gun is rolled over the barrel sight relationship will still be the same, that is the bore will still point at the same angle to intersect the line of sight, however the trajectory of the bullet will be affected by gravity and the relevant angles differently than when upright. The bullet will still leave the barrel at the same angle in relation to the bore/sight relationship, and will follow that angle until the bullet comes to rest instead of being pulled "down" to cross the line of sight at the initial and zero points as when fired slightly upward.
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory3.jpg
What this boils down to is that the bullet will cross the vertical sight plane (not the horizontal sight plane) closer to the muzzle (though not by a whole lot, depending on zero distance). It will be slightly low at close range because the bullet will essentially be launched horizontally instead of at a slightly upward angle and will therefore begin "falling" immediately upon exit from the barrel.
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory2.jpg
Here are rough numbers if the gun is rolled 90 degrees to the right and fired with an Aimpoint at lower 1/3 cowitness zeroed for 200 yards.
RANGE__DROP__L/R inches in relation to Dot
10______0.0___L 2.2
20______-0.1___L 1.7
30______-0.2___L 1.1
40______-0.3___L 0.6
50______-0.5___0
60______-0.7___R 0.6
70______-0.9___R 1.1
80______-1.2___R 1.7
90______-1.5___R 2.2
100_____-1.9___R 2.8
110_____-2.3___R 3.4
120_____-2.8___R 3.9
130_____-3.3___R 4.5
140_____-3.9___R 5.0
150_____-4.5___R 5.6
160_____-5.2___R 6.2
170_____-5.9___R 6.7
180_____-6.7___R 7.3
190_____-7.5___R 7.8
200_____-8.4___R 8.4
(The above is from a ballisitc calculator, but is very close to what happens in actual shooting, in my experience)
The rule of thumb is from 0 to about 75 hold high center torso.
From 75 to about 150 hold high on the inside pectoral.
From 150 to 200 hold on the inside shoulder (that is-the dot is in the middle of the shoulder, not the edge of the shoulder).
This will get you good central hits only needing to rmember three general areas- close, over 75, and over 150.
If you use a 100 yard/meter zero things are a little easier (I will just show 25 yard increments). Here is the ballisitc calculator's numbers for a TA-31, zeroed at 100 meters, 90 degree offest to the right, from the tip of the chevron.
RANGE__DROP__L/R inches in relation to chevron tip
0______0.0____L 2.8
25_____-0.1____L 1.6
50_____-0.5____L 0.4
75_____-1.1____R 0.7
100____-1.9____R 1.9
125____-3.1____R 3.0
150____-4.5____R 4.2
175____-6.3____R 5.4
200____-8.4____R 6.5
(Vertical plane cross-over at 60 yds)
It's a bit easier in that you can hold high center out to about 125, and outside that just hold on the inside shoulder joint.
Of course, with practice and experience you will get a better feel for your holds for greater precision if needed and longer distances, but I really consider 200 yards to be the limit of effective use due to the rapid drop you will see past that as well as the difficulty you will have in the precise range estimation you will need for hold-off and hold-over. Throw a little wind into the mix and you are pretty screwed.
People will tend to see a distinct offset at closer ranges (out to about 30 yards, depending on shooter skill) because they will be forming identifiable groups. At longer distances the groups tend to loosen up, as well as the fact that they are shooting very close to the vertical plane of the sights. Since there is essentially no offset to be accounted for out to about 100 (depending on zero), on steel it all seems to be right up the center (and for practical application it is good enough).
Just added some pics, hopefully I haven't been celebrating our independance too much to make something useful :D.
I have done a bit of shooting from weird positions to see what I can get out of them. To try to get solid info I did it with 1X optics and irons as well as with a 4X ACOG. There is a little bit of difference between the two categories, but mostly due to zero distance than magnification.
Here's how I explain it to guys that go through my courses-
When your rifle is in it's "normal" orientation the bullet travels upward at a determined angle to meet your line of sight at the initial point, continues up until it reaches the culminating point, and drops to meet the line of sight again at the true zero range (since we zero at the second cross-over with most optics to ensure maximum efficiency).
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory1.jpg
However, when we turn the gun sideways (let's take the urban/roll-over prone for the example since it is at or very close to a 90 degree offset), the bullet's trajectory will never cross-over the horizontal plane of the sight other than as it leaves the muzzle.
Why?
Beacuse when the gun is rolled over the barrel sight relationship will still be the same, that is the bore will still point at the same angle to intersect the line of sight, however the trajectory of the bullet will be affected by gravity and the relevant angles differently than when upright. The bullet will still leave the barrel at the same angle in relation to the bore/sight relationship, and will follow that angle until the bullet comes to rest instead of being pulled "down" to cross the line of sight at the initial and zero points as when fired slightly upward.
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory3.jpg
What this boils down to is that the bullet will cross the vertical sight plane (not the horizontal sight plane) closer to the muzzle (though not by a whole lot, depending on zero distance). It will be slightly low at close range because the bullet will essentially be launched horizontally instead of at a slightly upward angle and will therefore begin "falling" immediately upon exit from the barrel.
http://i296.photobucket.com/albums/mm174/Fail2Stop/Trajectory2.jpg
Here are rough numbers if the gun is rolled 90 degrees to the right and fired with an Aimpoint at lower 1/3 cowitness zeroed for 200 yards.
RANGE__DROP__L/R inches in relation to Dot
10______0.0___L 2.2
20______-0.1___L 1.7
30______-0.2___L 1.1
40______-0.3___L 0.6
50______-0.5___0
60______-0.7___R 0.6
70______-0.9___R 1.1
80______-1.2___R 1.7
90______-1.5___R 2.2
100_____-1.9___R 2.8
110_____-2.3___R 3.4
120_____-2.8___R 3.9
130_____-3.3___R 4.5
140_____-3.9___R 5.0
150_____-4.5___R 5.6
160_____-5.2___R 6.2
170_____-5.9___R 6.7
180_____-6.7___R 7.3
190_____-7.5___R 7.8
200_____-8.4___R 8.4
(The above is from a ballisitc calculator, but is very close to what happens in actual shooting, in my experience)
The rule of thumb is from 0 to about 75 hold high center torso.
From 75 to about 150 hold high on the inside pectoral.
From 150 to 200 hold on the inside shoulder (that is-the dot is in the middle of the shoulder, not the edge of the shoulder).
This will get you good central hits only needing to rmember three general areas- close, over 75, and over 150.
If you use a 100 yard/meter zero things are a little easier (I will just show 25 yard increments). Here is the ballisitc calculator's numbers for a TA-31, zeroed at 100 meters, 90 degree offest to the right, from the tip of the chevron.
RANGE__DROP__L/R inches in relation to chevron tip
0______0.0____L 2.8
25_____-0.1____L 1.6
50_____-0.5____L 0.4
75_____-1.1____R 0.7
100____-1.9____R 1.9
125____-3.1____R 3.0
150____-4.5____R 4.2
175____-6.3____R 5.4
200____-8.4____R 6.5
(Vertical plane cross-over at 60 yds)
It's a bit easier in that you can hold high center out to about 125, and outside that just hold on the inside shoulder joint.
Of course, with practice and experience you will get a better feel for your holds for greater precision if needed and longer distances, but I really consider 200 yards to be the limit of effective use due to the rapid drop you will see past that as well as the difficulty you will have in the precise range estimation you will need for hold-off and hold-over. Throw a little wind into the mix and you are pretty screwed.
People will tend to see a distinct offset at closer ranges (out to about 30 yards, depending on shooter skill) because they will be forming identifiable groups. At longer distances the groups tend to loosen up, as well as the fact that they are shooting very close to the vertical plane of the sights. Since there is essentially no offset to be accounted for out to about 100 (depending on zero), on steel it all seems to be right up the center (and for practical application it is good enough).
Just added some pics, hopefully I haven't been celebrating our independance too much to make something useful :D.