I've been trying to find the formula to optimize the size of a ballistic loophole and the optimal distance from the wall itself. All i really should need is dope, how high the scope is above the bore, and a ballistic chart right? If someone actually had the formula and could make it know id greatly appreciate it. I've also posted this question in a math forum and will post the results of my search.
Ballistic Loophole formula
- Thread starter Sentryau2
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Just use one of the ballistic programs that allows you to calculate different scope heights. You can set this up for basic or advanced if you want to
http://www.hornady.com/ballistics-resource/ballistics-calculator
http://www.hornady.com/ballistics-resource/ballistics-calculator
HorseSoldier
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Todd Hodnett at Accuracy 1st is the best SME on loophole shooting I've ever dealt with. I think he has a contact email on the company's website and might be willing to offer some advice if you're having problems.
Arizona_Mike
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Putting my $0.02 in before someone plays the OPSEC card :banghead:
The ballistic loophole involves applying boundary conditions to the bullet trajectory. It's basically how the angular span of things you want to shoot at distance project through a hole in near cover or concealment taking into account your distance from that concealment, the trajectory, and the 0-distance sight radius of your gun.
The closer your cover is to your near zero, the smaller the loophole can be.
As far as a formula, I suspect there are some simplified formulas or tables, etc. for specific firearms, cartridges, and bullets, that some might consider sensitive, but you can figure it all out with an on-line ballistic calculator.
Mike
PS. Saw someone on line that summarized loophole shooting as the art of not shooting your chrony. That's dead on.
The ballistic loophole involves applying boundary conditions to the bullet trajectory. It's basically how the angular span of things you want to shoot at distance project through a hole in near cover or concealment taking into account your distance from that concealment, the trajectory, and the 0-distance sight radius of your gun.
The closer your cover is to your near zero, the smaller the loophole can be.
As far as a formula, I suspect there are some simplified formulas or tables, etc. for specific firearms, cartridges, and bullets, that some might consider sensitive, but you can figure it all out with an on-line ballistic calculator.
Mike
PS. Saw someone on line that summarized loophole shooting as the art of not shooting your chrony. That's dead on.
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Arizona_Mike
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Using the power of High School Trig:
BD=Bullet diameter
SH=Sight height
LD=Loophole distance
LH=Loophole Height
NZ=Near Zero
HA=Holdover angle (negative for hold under).
H0=BD/2
H1=SH(NZ-LD)/NZ for LD <= NZ (practical cases) "Geometric Factor"
H2=-LD*Tan(HA) ~= -LD*Sin(HA) "Trajectory Factor" (negative for holdover, positive for holdunder).
LH= H0 + the greater of (H1 + H2 or H0) ~= H0 + H1 + H2 ~= H1 + H2
H1 is the simple triangular interpolation of the sight radius onto the Loophole (we can consider the trajectory linear at such short distances). H2 is an amount you can shrink the loophole at the top for holdover (you don't need the whole scope field of view to see) or the amount you have to add to the loophole height at the top to be able to see the target in a holdunder situation. H1 is 0 at the near zero and far zero.
Mike
PS. If you are measuring holdover in radians, you can use the small angle approximation rule and say H2=-LD*HA. If you are not using radians (deg, MoDeg, real MilliRadians or the Nato or Commie approximation thereof, you need the appropriate version of the small angle approximation for that system).
BD=Bullet diameter
SH=Sight height
LD=Loophole distance
LH=Loophole Height
NZ=Near Zero
HA=Holdover angle (negative for hold under).
H0=BD/2
H1=SH(NZ-LD)/NZ for LD <= NZ (practical cases) "Geometric Factor"
H2=-LD*Tan(HA) ~= -LD*Sin(HA) "Trajectory Factor" (negative for holdover, positive for holdunder).
LH= H0 + the greater of (H1 + H2 or H0) ~= H0 + H1 + H2 ~= H1 + H2
H1 is the simple triangular interpolation of the sight radius onto the Loophole (we can consider the trajectory linear at such short distances). H2 is an amount you can shrink the loophole at the top for holdover (you don't need the whole scope field of view to see) or the amount you have to add to the loophole height at the top to be able to see the target in a holdunder situation. H1 is 0 at the near zero and far zero.
Mike
PS. If you are measuring holdover in radians, you can use the small angle approximation rule and say H2=-LD*HA. If you are not using radians (deg, MoDeg, real MilliRadians or the Nato or Commie approximation thereof, you need the appropriate version of the small angle approximation for that system).
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Oh man I'm in neck deep. Never was good at math but I guess its time to take a couple classes.
I really appreciate the help Mike, I've been hunting for this formula for a while. I could always use a ballistics calculator but nothing beats being able to do it by hand.
I really appreciate the help Mike, I've been hunting for this formula for a while. I could always use a ballistics calculator but nothing beats being able to do it by hand.
Arizona_Mike
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I'm took a very complex problem and solved it easily but still precisely by solving it in terms of holdover angle (a careful choice of coordinates often makes super hard problems simple). The advanced math (and drag models which are a mix of art and science) come in finding that holdover angle. Fortunately that is usually known already.
I suspect the military have all kinds of neat tricks and rules of thumb specific to their equipment that they can memorize and use in the field.
For example, I'll make one up on the spot:
For a M4/M16/AR15 type rifle, the bottom of an EOTech reticle circle sighted in at 100 yards happens to be your 7-yard zero.
If you are about 20 feet from your loophole and the top of the loophole does not block your view of the target and the bottom of the loophole appears below that circle, you are good to go. If not schooch your butt a little closer. If the space in generous, you can move back. From what I have read, soldiers in urban combat often use a loophole in an adjacent room or down a hallway.
I'd wager real snipers and sharpshooters know which of their mil dots correspond with various near zero distances and can tell in a second if they are going to put a shot through a loophole.
I suspect the military have all kinds of neat tricks and rules of thumb specific to their equipment that they can memorize and use in the field.
For example, I'll make one up on the spot:
For a M4/M16/AR15 type rifle, the bottom of an EOTech reticle circle sighted in at 100 yards happens to be your 7-yard zero.
If you are about 20 feet from your loophole and the top of the loophole does not block your view of the target and the bottom of the loophole appears below that circle, you are good to go. If not schooch your butt a little closer. If the space in generous, you can move back. From what I have read, soldiers in urban combat often use a loophole in an adjacent room or down a hallway.
I'd wager real snipers and sharpshooters know which of their mil dots correspond with various near zero distances and can tell in a second if they are going to put a shot through a loophole.
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Why would a normal person need to take a carbine class?
Why would a normal person need to shoot out to 1000 yards?
Sometimes it is just about the fun involved.
Sam1911
Moderator Emeritus
Why would a normal person need a gun that can shoot 1,000 yards, or fire full auto, or whatever else?
Tenche Coxe had a great quote about it back around the late 1780s.
And besides, who wants to be "normal?" "Normal" is boring!
Tenche Coxe had a great quote about it back around the late 1780s.
And besides, who wants to be "normal?" "Normal" is boring!
because we normal people also shoot rifles around objects and we don't want to accidentally hit something in the path, like a tree branch or wall or rock etc.
granted, MOST people just move well clear of those objects so you don't have to calculate anything. but sometimes you don't have a choice.
sentry and mike, there is more than one way to compute this, but i just use the old junior high algebra "slope intercept form" y = mx + b and built a quick excel spreadsheet to calc it for me.
it's not hard to figure out, and it only works to your zero distance, so it's not perfect. basically, i find the slope of my trajectory between the muzzle and zero distance by first figuring out how much the dope i have on my rifle subtends at the zero distance, and then adding that to my height over bore (rise) and dividing that by the zero distance (run). then if i want to find the distance to the optimally small loophole, I solve for x and if i want to find how tall the loophole needs to be at a given distance i solve for y.
pretty simple, but it doesn't exactly take into account the small drop from gravity between the muzzle and your zero distance, so it's not perfect. i mean, it assumes a straight line, where the line is curved up usually an inch or so
HorseSoldier
Member
. . . No honest man needs a rifle that can shoot through small holes . . .
I certainly hope thats a joke horsesoldier my bone stock savage .22 can do it, the marlin 30-30 can do it, my sig m4 can do it. Anygun is capable of it anyone is capable of it. I just needed the math. Next week I plan to get some serious trigger time in practicing this.
EDIT-I think its a bit of a shame it took me this long to find information on this topic.
EDIT-I think its a bit of a shame it took me this long to find information on this topic.
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No honest man needs a rifle that can shoot 1000 yards
No honest man needs a car that can go over 90 mph
Uncle Mike
Member
Most of, or maybe I should say, in the real world, you'll need to 'actually' shoot for the loophole. There is not a widely known 'formula' that is commonly used to figure the distance.
Two shots and you can figure the distance....exactly!
As was said earlier, most any of the ballistic calculators can give you a pretty/reasonably, close approximation of the convergence distance.
Arizona_Mike
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@jdduffy:
1. Not shooting your chronograph.
2. Hunting blind.
3. WotRoL situations (sure it is unrealistic, the police would never abandon entire neighborhoods or cities for 4 or 5 days at a time. Oh nevermind
).
@taliv: what you are describing is my H1 term. If you are only shooting holdover distances (past your far zero) it works in the sense that it gives you room to space. If you are shooting at a hold under distance (between zeros--only matters for small targets) you need a slightly larger loophole.
Mike
PS. I am actually impressed no one started ranting about OPSEC which has occured on this very forum and others when loopholes are raised.
1. Not shooting your chronograph.
2. Hunting blind.
3. WotRoL situations (sure it is unrealistic, the police would never abandon entire neighborhoods or cities for 4 or 5 days at a time. Oh nevermind
).@taliv: what you are describing is my H1 term. If you are only shooting holdover distances (past your far zero) it works in the sense that it gives you room to space. If you are shooting at a hold under distance (between zeros--only matters for small targets) you need a slightly larger loophole.
Mike
PS. I am actually impressed no one started ranting about OPSEC which has occured on this very forum and others when loopholes are raised.
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Art Eatman
Moderator In Memoriam
If this sort of figuring is thought to be some big secret, believers should be sent back to the State Home For The Bewildered. Dunno why anybody thinks that highschool math is secret.
HorseSoldier
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Uh, yeah -- riffing on Bill Ruger's (in)famous "no honest man needs more than 10 rounds" comment.
You'll notice up thread I also suggested a subject matter expert who might be able to offer advice on the topic.
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