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Old August 13, 2019, 08:55 AM   #26
Bart B.
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Semantics are muddying the waters we're wading in.

Any 3 of these 4 (eye, rear sight, front sight, target aimpoint) not physically aligned on one axis equals parallax.

All four(and the trajectally pointed barrel) must be aligned on one axis if you want to hit point of aim with the bullet.

Last edited by Bart B.; August 13, 2019 at 09:16 AM.
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Old August 13, 2019, 09:33 AM   #27
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Bart, I don't think mere semantics are the source of the confusion here.

Quote:
Any 3 of these 4 (eye, rear sight, front sight, target aimpoint) not physically aligned on one axis equals parallax.
A misalignment of the latter three does not describe parallax, only a misalignment of the sights. Line a rifle up on target and move the muzzle of the rifle an inch left, but don't move your head. The sights now are not aligned on the target, but that's mere misalignment, not parallax error.

Parallax is

Quote:
the effect whereby the position or direction of an object appears to differ when viewed from different positions
https://www.lexico.com/en/definition/parallax

Only a viewer can view these objects from different positions. When a viewer sees the same rifle in the same position and moves his head, he views from different positions. A parallax adjustment in an optic eliminates or reduces the change in sight picture (parallax error) at specific distances and caused by the viewer's head movements.

Iron sights don't limit parallax error caused by head movement (movement of the viewer), but limit the head movement possible while still maintaining a correct sight picture.

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Old August 13, 2019, 10:12 AM   #28
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Whatever ...... ..... .... ... .. .
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Old August 13, 2019, 10:43 PM   #29
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"Aim point," to me, is the place on target the place on target the front sight is aligned to in the sight picture. It's the far end of the straight line of sight from the aiming eye through the rear sight to the front sight then to some place on target.
I agree with that. However, if there is NOT a straight line from the eye through the rear sight to the front sight to the target, then what is the aim point?

When the eye is not aligned with the sights, then they do not form a straight line.

That's what I'm saying when I say that if the sights are not aligned with each other and with the eye, then there isn't an aim point.

If the misalignment is SMALL, then there is an aimpoint, but it's impossible to say if that misalignment is due to the eye being out of line with the sights (which might be loosely interpreted as parallax) or the sights being out of line with each other because the effect is exactly the same in either case.
Quote:
A point on the target upon which the firearm is aimed.
Agree. But if the eye is not aligned with the sights and the sights aren't aligned with each other then I would say the gun is not aimed at anything. Right now there is a gun in my safe and although one could draw a line through the sights, it wouldn't go through my eye or to any target--it's not aimed at anything in any reasonable sense of the word.
Quote:
The exact point (at the target) on which the shooter aligns the firearm’s sights.
Agree. And from that definition, it follows that if the sights aren't aligned then there's no aim point.
Quote:
The visual image observed by the shooter when the firearm sights are properly aligned on the point-of-aim.
Again, I agree. But what is it called when the sights aren't properly aligned?
Quote:
The aiming eye does not automatically (subconsciously?) align anything to the visual center of the aperture in the rear sight. Nor the notch in an open rear sight. This age-old myth continues to surface in the shooting sports.
I've never seen any tendency for the eye to "automatically" align anything in the notch of a rear sight.

However, I have noticed some tendency for the eye to try to center things in a well-designed aperture sight. Conversely, I've seen poorly sight systems where the eye tries to center the wrong thing in the rear aperture. One example of this is putting a rear aperture sight on a rifle that has a protective hood that isn't round over the front sight. The non-round hood tends to interfere with the eye's attempt to center the bead in the aperture, and removing the hood tends to improve on-target results.
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Any 3 of these 4 (eye, rear sight, front sight, target aimpoint) not physically aligned on one axis equals parallax.
I disagree. No definition of parallax I've seen or that you've quoted says anything like that.

Look, I think you have a point to this thread and the questions you asked.

Maybe instead of arguing about why it does or doesn't make sense to try to incorporate sight misalignment into the definition of parallax we could skip to the point of why you started the discussion.
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Old August 14, 2019, 01:15 PM   #30
Bart B.
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I'll try to simplify my point.

After the rear sight is zeroed for target range with the LOS from eye through rear and front sight centers to point of aim on target, for every MOA the LOS is off center in the rear sight thereafter the shot will go one MOA in that direction because the LOF moved that much relative to the LOS. Field of view through the rear sight aperture can be a few to several dozen MOA depending on aperture & eye iris diameters and eye relief from aperture.

Easy to see if you can shoot with aperture sights under MOA for a couple dozen consecutive shots. 1 MOA in the rear sight aperture is sight radius divided by 3600.

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Old August 14, 2019, 02:45 PM   #31
Aguila Blanca
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You are not describing parallax.

Parallax is optical distortion. Parallax applies only to scopes, not to open sights or single-plane optics. Parallax error is when the shooter has the crosshairs centered on the target POA, but the image is not correctly aligned with the axis of the bore due to the shooter's eye being off the axis of the scope. For any scope, parallax error does not apply at a specified distance, and does apply at other distances. Scopes that allow adjustment of the shooting distance can be adjusted to eliminate parallax error at multiple distances. (So-called "AO" -- for Adjustable Objective) scopes.)
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Old August 14, 2019, 03:19 PM   #32
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Aguila,

A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use a needle-style speedometer gauge. When viewed from directly in front, the speed may show exactly 60; but when viewed from the passenger seat the needle may appear to show a slightly different speed, 55 for example, due to the angle of viewing. No optics nor lenses whatsoever.

None of the dictionaries listing "parallax" state it's limited to optics and lenses.

No scope with the range focus knob opposite the windage knob have a user adjustable objective lens; it's fixed in place.

When the shooter has the crosshairs centered on the target POA, the image is never aligned with the axis of the bore.

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Old August 14, 2019, 03:34 PM   #33
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Quote:
Originally Posted by Bart B.
None of the dictionaries listing "parallax" state it's limited to optics and lenses.
Parallax is a phenomenon present whenever a viewer watches two objects at different distances and changes his position. Every child who looked out a car window at plowed fields has seen it.

While the phenomenon is present in many situations, it is a parallax error only where an optic designed to present a target and crosshair on the same plane fails to actually present them on the same plane.

Misalignment of iron sights doesn't give rise to this error because those systems don't present a viewer with target, front post and rear aperture on a single plane, ever. Therefore, that misalignment is not a parallax error.

You are absolutely correct that an alignment error will cause a round to land at a different spot relative to the front post, but since it doesn't occur where the sight picture is correct, the error isn't the result of parallax.
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Old August 14, 2019, 03:39 PM   #34
Bart B.
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Quote:
Originally Posted by zukiphile View Post
While the phenomenon is present in many situations, it is a parallax error only where an optic designed to present a target and crosshair on the same plane fails to actually present them on the same plane.

Misalignment of iron sights doesn't give rise to this error because those systems don't present a viewer with target, front post and rear aperture on a single plane, ever. Therefore, that misalignment is not a parallax error.
Yes, they do present a viewer with target, front post and rear aperture images on a single plane . On the retina of the aiming eye. Lateral displacement of each is easily seen.

The eye retina acts like the second image plane in a scope sight where the first focal plane image and reticle are focused.

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Old August 14, 2019, 05:23 PM   #35
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Quote:
Originally Posted by Bart B.
Yes, they do present a viewer with target, front post and rear aperture on a single plane . On the retina of the aiming eye. Lateral displacement of each is easily seen.
Emphasis added.

Let's unpack that. The rear sight is just an inch or two from the eye. That's the first focal distance for the viewer, but we don't really focus on it. The front post will be a couple of feet away. That's another focal distance, and the element on which we are supposed to focus. The target will be 25, 50, 100, 200 etc yards away. That's a third focal distance even though we aren't supposed to focus on it. Iron sights do not present a viewer with rear sight, front post and target on a single plane, but three distances only one of which we hold in focus.

In contrast, a scope may present the crosshairs and target on a single focal plane that is within a foot of the eye.

That poor alignment of iron sights can be spotted is true, and demonstrates why that condition isn't parallax error, which will not be easily spotted in a scope unless the viewer moves his head.


If your point is that the best accuracy requires a consistent hold and head position for both a scope and iron sights, I doubt anyone would argue the point.

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Old August 14, 2019, 05:40 PM   #36
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I don't think the tiny out of perfect focus distance each iron sight system part puts on the eye retina is enough to matter. My concern is their misalignment at right angles to the LOS. Human eye lens focal length is too short to matter for me.j

Interesting article on aperture sight parallax:

https://www.google.com/search?q=Para...obile&ie=UTF-8

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Old August 14, 2019, 09:34 PM   #37
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Here's the link to the article:
http://dougkerr.net/Pumpkin/articles/Aperture_Sight.pdf
Quote:
Originally Posted by Bart B.
After the rear sight is zeroed for target range with the LOS from eye through rear and front sight centers to point of aim on target, for every MOA the LOS is off center in the rear sight thereafter the shot will go one MOA in that direction because the LOF moved that much relative to the LOS. Field of view through the rear sight aperture can be a few to several dozen MOA depending on aperture & eye iris diameters and eye relief from aperture.
When you say LOS, are you talking about moving the eye? Because if one aligns the sights on the target properly and only moves the eye, there will be no change on the target unless the gun is moved too.

If you mean that moving the eye off center from the rear sight and then lining up the front sight on the target (but still keeping it within the rear sight aperture from the shooter's perspective) then the article you linked to states, and provides test data and rationale to support the assertion, that such a movement will have no significant effect on the point of impact.

From the article:
"The second target shows the result for a group fired with the front sight intentionally offset towards the upper edge of the aperture. The “ears” of the front sight were positioned so that they were near the edge of the aperture. This magnitude of offset constitutes a “gross misalignment” of the sights in terms of the standard method of aiming, and under the “common wisdom” would be expected to result in shots that would be displaced from the intended point of aim by a considerable amount because of parallax. However, as can be seen from the target, this “misalignment” of the front sight in the aperture did not result in a significant shift of the bullet group on the target. "
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Old August 15, 2019, 07:35 AM   #38
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Yes, the article I linked to states, and provides test data and rationale to support the assertion, that "such a movement will have no significant effect on the point of impact."

How much does the LOF to LOS angle have to be before it becomes significant?

What's the angle between "zero" and "no significant" effect.

It's easy to see a half MOA parallax error in a magnified image in a scope sight. The visual amount seen by the eye with a 10X scope is ten times as big as seen by an unaided eye. Human eye angular resolution varies from 1/2 to 1 arc minute. With a 10X scope, the human eye can see 1/20th to 1/10th MOA parallax error between LOS and LOF. Ten times those values with metallic sights.

If one can really put the line of fire precisely to the same point on target with metallic sights for every shot fired, why do benchresters magnify the sight picture a few dozen times with a telescope?

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Old August 15, 2019, 08:06 AM   #39
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Quote:
Originally Posted by Bart B.
Interesting article on aperture sight parallax:
It prompted me to check this at 20 yards (the sun wasn't up and I had to do this indoors). With the small aperture I detected no shift, but with the large aperture, the shift with head movement was considerable.

The authors did a good job of describing how the smaller aperture determines the alignment of the image the eye will pick up. This explains why my accidentally using the large aperture for sighting in resulted in a different point of impact last week even though the group was a normal (for me) size. The small aperture may have helped conceal from me an error in my eye's alignment that the larger aperture didn't conceal.

Even if I had perfect alignment, I would still need the smaller aperture for the better depth of field.

It is an interesting article.
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Old August 15, 2019, 10:21 PM   #40
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Quote:
How much does the LOF to LOS angle have to be before it becomes significant?
1. You never explained what you meant by your initial statement above LOF/LOS.

2. Using conventional definitions for LOF and LOS, any angle between them should be detectable on the target as long as it's large enough to be detectable on the target.

3. Neglecting LOF and LOS and just talking about the article and using the terminology it uses, according to the article, apparent misalignment between the sights can be expected to have a different effect on target with open sights than it does with aperture sights--both, of course, being metallic sights.

Any sight misalignment in open sights should have an immediate effect on the target, one that can be calculated--but sight misalignment with a typical metallic sight system is not really parallax, as discussed in depth above. Things might be different with aperture sights, according to the article--possibly because a sufficiently small aperture acts something like a lens.

And, of course, things are different yet when discussing optical sights where parallax in the conventional sense obviously comes into play.

I know you're trying to get at something, but your unconventional definitions for the terms you are using are making it really difficult to even understand your questions. let alone answer them in a way that might lead to learning. If the goal is to help people understand things that they currently don't understand, the first step is communication and that means using conventional meanings for the important terms in the discussion.
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Old August 16, 2019, 05:01 PM   #41
Bart B.
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Parallax does not require optical lenses. It comes from an old Greek word
parallaxis. Look it up.

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

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Old August 16, 2019, 05:11 PM   #42
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Quote:
Visual parallax does not require optical lenses.
I didn't say it did.
Quote:
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.
Agreed. Agreed since the very beginning of the thread.
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Old August 16, 2019, 05:25 PM   #43
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Things are not different with aperture nor open sights. A small aperture or notch does not act like a lens, light going through it doesn't change medium like glass to air lens curved surfaces do to change its direction. It's all air.

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Old August 16, 2019, 05:42 PM   #44
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According to the paper you quoted, they are quite different with aperture sights.

According to what I can see with my own eyes, they are quite different with open sights, but for a different reason.
Quote:
A small aperture or notch does not act like a lens...
Ever hear about a pinhole camera?

https://www.quora.com/How-can-a-pinhole-act-as-a-lens

https://www.howtogeek.com/161794/how...igital-camera/
"How can you have a lens with no glass? With a traditional glass lens, the optical elements are shaped and polished so that the lens is able to collect light over a wide area and pass that light through the barrel of the lens onto the focal plane of the camera body (where the film or sensor is located), while preserving the image without distortion. With a pinhole “lens” the same effect is achieved, but through different means. Because the opening, or aperture, or the pinhole lens is so very tiny it allows only a very small amount of light to pass through it. The rays of light and the tiny amount that passes through the pinhole opening stay almost perfectly parallel with each other (a feat the glass-based lens needs carefully machined and polished elements to achieve)."
https://electronics.howstuffworks.com/question131.htm
"The pinhole in a pinhole camera acts as the lens. The pinhole forces every point emitting light in the scene to form a small point on the film, so the image is crisp. The reason a normal camera uses a lens rather than a pinhole is because the lens creates a much larger hole through which light can make it onto the film, meaning the film can be exposed faster."
I agree that a notch is something else entirely from an aperture.

We're wandering farther and farther away from your initial questions and whatever purpose you had in asking them. This is still an interesting discussion, but I can't help thinking that this isn't what you intended.
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Old August 16, 2019, 06:32 PM   #45
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Quote:
Originally Posted by Bart B.
Things are not different with aperture nor open sights. A small aperture or notch does not act like a lens, light going through it doesn't change medium like glass to air lens curved surfaces do to change its direction. It's all air.
Emphasis added.

Your linked article aptly explains the difference. A smaller aperture produces a smaller image than the eye's "aperture" and masks some of the shooter's alignment error. An open sight doesn't.

I shoot pistol with an open sight, and an iron sight rifle. I can assure you that the aperture is doing something the open sight isn't.
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Old August 16, 2019, 09:44 PM   #46
Bart B.
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A smaller aperture produces a smaller field of view than the eye's "aperture" and masks some of the shooter's view further from point of aim. Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused. No alignment error is masked.

Pin hole cameras do not act like a lens, they don't bend and focus light rays. They're identical to aperture rear sights as far as rays of light going through them. A ray of light entering a tiny or huge hole exits at the same angle it entered.

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Old August 17, 2019, 12:16 AM   #47
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Communication requires common language. If you're going to make up your own definitions for things and insist upon them in the face of evidence to the contrary, it's impossible to communicate.

https://en.wikipedia.org/wiki/Pinhole_occluder

"A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light,"

https://en.wikipedia.org/wiki/Pinhole_camera
"In the region of near-field diffraction (or Fresnel diffraction), the pinhole focuses the light slightly, and the resolution limit is minimized when the focal length f (the distance between the pinhole and the film plane) is given by f = s2/λ. At this focal length, the pinhole focuses the light slightly, and the resolution limit is about 2/3 of the radius of the pinhole. The pinhole, in this case, is equivalent to a Fresnel zone plate with a single zone. The value s2/λ is in a sense the natural focal length of the pinhole."
http://hilaroad.com/camp/projects/pinhole.html
"A tiny hole (less then 1 mm), focuses light passing through it, much the same way a lens does."
https://www.flickr.com/groups/844582...7604778403047/
"Pinholes, like (uncorrected) lenses will only focus one wavelength "perfectly"."
https://www.asu.edu/courses/phs208/p...a/camera.shtml
"But the aperture itself can function as a lens."
https://www.exploratorium.edu/tinker...-modesto-tamez
"To start off our exploration, Modesto demonstrated how a pinhole can focus light without a lens. "
But you know, I kind of think you were already completely aware of this property of apertures. Just a guess on my part...
Quote:
Originally Posted by Bart B.
Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused
Quote:
No alignment error is masked.
The paper you linked to states that an aperture sight system masks eye alignment errors.

Bart, where were you going with the questions you posed at the beginning of the thread??? Can we reset back to the beginning of the thread, start over with common terminology and accepted definitions and maybe get this back on track?
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Old August 17, 2019, 06:23 AM   #48
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Quote:
Originally Posted by Bart B.
A smaller aperture produces a smaller field of view than the eye's "aperture" and masks some of the shooter's view further from point of aim. Everything seen through the aperture will also be seen the exact same way relative to each other and the LOS with the eye alone but darker and better focused. No alignment error is masked.
The underlined language is correct but makes a different point. An alignment error is masked where it is concealed from a viewer because the point of perspective is fixed despite movement of the viewer's eye. The bold assertion is incorrect. In the article, that point is explained at page 6.

Quote:
Originally Posted by Burdge and Kerr, p.6
Now, if we move our eye from side to side a little bit, our first thought is that the point of perspective would change. But since the point of perspective is at the center of the sight aperture, and that is fixed, the point of perspective does not move.
In pages 7 and 8, the authors explain the qualities of a small aperture sight that are not like an open sight.

Last edited by zukiphile; August 17, 2019 at 07:10 AM.
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Old August 17, 2019, 08:28 AM   #49
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Maybe someone can explain why my shots aimed with aperture front and rear sights having a 29 to 38 inch radius never pointed the barrel such that bullets went to call (for rifle-ammo accuracy) at ranges from 50 to 1000 yards unless their centers were all on the same visual axis from eye to bullseye target.

I'm not the only one who would like to know.
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Old August 17, 2019, 11:50 AM   #50
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Quote:
Originally Posted by Bart B.
Maybe someone can explain why my shots aimed with aperture front and rear sights having a 29 to 38 inch radius never pointed the barrel such that bullets went to call (for rifle-ammo accuracy) at ranges from 50 to 1000 yards unless their centers were all on the same visual axis from eye to bullseye target.
Bart, could you re-phrase that? I'm guessing there is some idiomatic material here, because I'm gleaning that you shoot rimfire out to 1000 yards, and the bullets never went to call ( I don't know what "went to call" means) unless their (I don't know the antecedent for "their") unless their centers were all on the same visual axis.

The excerpt I quoted above explains why the center of the eye need not be on the same axis as the aperture front sight and POA if the aperture is small enough.

The concept of a single axis involves a specific point on the eye. At page 5, the article addresses that idea.

Quote:
This at first seems a little over-simplistic. After all, the eye doesn’t just regard the world through the center of the entrance pupil, but rather through all of it. So shouldn’t we consider that the eye has many “vantage points”, one for every imaginable location within the entrance pupil?

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