AR-15 Zeros and Trajectories

[Molon]

Thoughts?

From my original post of this thread . . .



Choose your zeroing scheme based on the pertinent facts; not nonsense about “shooting through a cone.” When shooting at human targets, in the grand scheme of things there isn’t going to be any practical difference between a point of impact that has a negative deviation from the point of aim, (e.g. the bullet strikes 1.5” below the point of aim) and a point of impact that has an equal positive deviation from the point of aim (e.g. the bullet strikes 1.5” above the point of aim.) In other words, the absolute value of the point of impact from the point of aim (how far the point of impact deviates from the point of aim, regardless of whether it is a positive or negative deviation) is what we need to be concerned about. Therefore, one of the main points to consider when choosing a battle-sight-zero is this: What zeroing scheme produces the smallest absolute values for the deviations of the points of impact from the point of aim, over the distance that we reasonably expect to engage a human target in our intended usage?

The chart below illustrates the above concept. The chart compares the absolute values of the deviations of the points of impact from the point of aim (0.0 inches on the graph being the point of aim/line of sight) for a 50-yard-zero and a 100-yard-zero, using Hornady 5.56 TAP T2 ammunition.







As you can see in the graph above, from the muzzle (0 yards) to approximately 62 yards, the 50-yard-zero has a slight advantage over the 100-yard-zero. Between the distances of 62 yards and 165 yards, the 100-yard-zero has the advantage. From the distance of 165 yards out to the 250 yards shown in the graph, the 50-yard-zero has a distinct advantage over the 100-yard-zero. Choose your zeroing scheme based on the pertinent facts.



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[lethal dose]

Hope all's well, guys. I've reviewed the thread for performing a 100 yd zero on an A2 upper, but don't understand how to translate it to an A2 detachable CH. Can you give me a few pointers? Many thanks.

[Molon]

Hope all's well, guys. I've reviewed the thread for performing a 100 yd zero on an A2 upper, but don't understand how to translate it to an A2 detachable CH. Can you give me a few pointers? Many thanks.

from the original post:

* E.T.A.

All click references should be doubled when using detachable carry handle sights.

[Lamented]

Molon not sure if this was covered here. Just wondering what you think of this. And what distance do you use for sighting in?

http://www.thenewrifleman.com/maximu...-of-ar15-zero/

[lethal dose]

from the original post:

I should have expounded. I saw that and, unfortunately, I simply don't understand it. If you don't mind, could you spell that out in a bit more detail? Thanks!

[Amicus]

I should have expounded. I saw that and, unfortunately, I simply don't understand it. If you don't mind, could you spell that out in a bit more detail? Thanks!

Try this:

We are only talking about carry handle style rear sights. With fixed carry handle sights, the lowest marked elevation setting is (usually) "8/3". When you turn the elevation wheel clockwise to get to the marked setting "4", there will be THREE distinct clicks, or stopping points. The third one is at marked setting "4".

If you are using a removable carry handle, the lowest marked setting is usually "6/3". When you turn the elevation wheel clockwise to get to setting "4", there will be SIX clicks, or stopping points, with the sixth one being the setting marked "4". In other words, there are double the number of clicks (compared to fixed carry handles) to get from one marked elevation to the next marked elevation.

I have heard of removable carry handles with the fixed carry handle-standard three clicks between "3/6" and "4", but those are unusual.

This is important for the RIBZ because, when you adjust the rear sight settings so that the marked settings are shifted and your lowest possible setting is now FOUR clicks counterclockwise from the "3/8" setting, it will usually require EIGHT clicks of counterclockwise adjustment from "3/6" to have the same result with removable carry handles.

[lethal dose]

There's not an emoji that indicates something going way over its head, is there?

Try this:

We are only talking about carry handle style rear sights. With fixed carry handle sights, the lowest marked elevation setting is (usually) "8/3". When you turn the elevation wheel clockwise to get to the marked setting "4", there will be THREE distinct clicks, or stopping points. The third one is at marked setting "4".

If you are using a removable carry handle, the lowest marked setting is usually "6/3". When you turn the elevation wheel clockwise to get to setting "4", there will be SIX clicks, or stopping points, with the sixth one being the setting marked "4". In other words, there are double the number of clicks (compared to fixed carry handles) to get from one marked elevation to the next marked elevation.

I have heard of removable carry handles with the fixed carry handle-standard three clicks between "3/6" and "4", but those are unusual.

This is important for the RIBZ because, when you adjust the rear sight settings so that the marked settings are shifted and your lowest possible setting is now FOUR clicks counterclockwise from the "3/8" setting, it will usually require EIGHT clicks of counterclockwise adjustment from "3/6" to have the same result with removable carry handles.

[Amicus]

There's not an emoji that indicates something going way over its head, is there?

My last try with an analogy:

Imagine a car with a three speed transmission: low, medium and high gears. To get from 0 to top speed, you move through three gears.

Now, imagine the same car, but with a six speed transmission. To get from 0 to top speed, you move through six gears. You are not going any faster than with the three speed transmission, but you have to go through DOUBLE the number of gears.

[Molon]

Just wondering what you think of this.

http://www.thenewrifleman.com/maximu...-of-ar15-zero/

Not much.

From the article: “Typically M193 is considered a 1.5 to 2 MOA bullet. . .”

That statement alone, demonstrates his lack of knowledge/experience on the subject matter.

My evaluation of four different M193 loads (at the link below) shows that M193 loads only average approximately 3 MOA . . . and that evaluation was conducted using heavy barrels shot from a bench-rest; not standard barrels shooting from field positions.



Attack of the (M193) Clones







Also, his thinking is based on shooting at old-fashioned B-27 targets. That’s another indicator of his lack of knowledge/experience on the subject matter.



B-27 target . . .







How often does an armed criminal/enemy combatant who is intent on inflicting death or grave bodily harm on a law abiding citizen/law enforcement officer/soldier, stand out in the open, squarely facing you, with his hands at his side and holding perfectly still (which is what is depicted in a scenario with the unrealistic B27 targets) while allowing you to shoot at him and all the while not shooting back at you?

The Front Sight target pictured below is an “accurate representation of human dimensions taken from medical cadaver studies and 3000 x-ray studies.” This target represents a much more realistic aiming area that you would have available to shoot at on a criminal/enemy combatant who is shooting at you from behind cover. As you can see, the room for error on the part of the law abiding citizen/LEO/solder is far smaller with this target than that depicted in typical law enforcement/military training targets; particularly since our objective is not “just to hit the target,” but to make multiple center of upper thoracic cavity/central nervous systems hits (depicted by the “5” scoring zones on the target below).









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[Molon]

Try this:

We are only talking about carry handle style rear sights. With fixed carry handle sights, the lowest marked elevation setting is (usually) "8/3". When you turn the elevation wheel clockwise to get to the marked setting "4", there will be THREE distinct clicks, or stopping points. The third one is at marked setting "4".

If you are using a removable carry handle, the lowest marked setting is usually "6/3". When you turn the elevation wheel clockwise to get to setting "4", there will be SIX clicks, or stopping points, with the sixth one being the setting marked "4". In other words, there are double the number of clicks (compared to fixed carry handles) to get from one marked elevation to the next marked elevation.

I don't know that I can explain it any better than Amicus just did. The only other thing I can suggest is to find find someone with a fixed carry handle upper receiver, and put that next to your removable carry handle sight and start playing with the elevation drums. Then maybe it will become clear after actually seeing it in person.



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