M-4 / M-16 iron sights question.


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LordOfThetards
February 2, 2011, 07:34 PM
So, i'm new here - i basically found a gun forum that i felt would settle a debate i got into w/ my platoon sergeant today.

Some statements, some questions...

Question: How much of a difference does adjusting the rear sight all the way left or right (relative to center) make on the target. IE how much does adjusting it full left move the impact point on a 25m zero target.

He claims (and i was pretty strongly disagreeing with) that anyone can pick up any rifle that has been 'properly zeroed' and fire fine w/ it (for the purposes of this discussion, land 5 out of 6 consecutive shots in the 'zero area' on an M4 / M16 25m zero target.

I'm pretty sure I'm in the right here, and all that really needs to be illustrated is the numbers: ideally i would posit that a weapons that's adjusted full left would cause someone who zeroed on a weapon that was adjusted full right to miss the black entirely, and have a way to explain why, and by (approximately) how much.

The reward is 2 days off of my choosing -- he was pretty confident..

thanks in advance for the help,

chuck

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txhoghunter
February 2, 2011, 07:54 PM
Um, I'm no expert with irons on an AR, but I would actually agree with your platoon sergeant here.

If the irons are adjusted correctly to how the RIFLE shoots (meaning if it is all the way left, the rifle is missing right), anyone can shoot it accurately and hit the zero zone. Any miss would be the fault of the shooter flinching, pulling, etc.

I think, that the sights are zeroed for the rifle NOT the shooter

thralldad
February 2, 2011, 08:08 PM
Battlesight zero will get you on paper. This centers sights to weapon. From there you zero to your eye and cheekweld. I have picked up plenty of other people's properly zeroed weapon and can hit most targets.

Floppy_D
February 2, 2011, 08:12 PM
Take the distance from the front post to the target, and divide it by the sight radius (distance between front and rear sight.) Lateral movement of the rear sight will affect the POI by that ratio. So if your sight radius is 14.5" and the distance is 25yds (900") then your ratio is a hair over 62:1. Multiply the distance that rear sight can move left or right of center (let's say an 1/8th of an inch) and that'll give you over 7" in either direction.

What I'd want to know to settle the arguement, is what kind of grudge your Plt Sgt is gonna hold for you running in and proving him wrong with an internet thread. I think the best bet would be to drag a few random rifles to the range in lieu of an honest workday, test the theory, and discuss your findings over a beer at the E-club. If you guys are really good you could convince your COC that this is an idea worth researching, and maybe both of ya would earn a day off. :)

essayons21
February 2, 2011, 08:12 PM
If the cheek weld is the same, the zero should work between different shooters. This is one of the reasons the army teaches nose to charging handle.

Battlesight, or mechanical zero only puts the sights in the center of their adjustment range. If the weapon is new and well built, it should also put you on paper... but not always, especially on older and frankenstein weapons.

BullfrogKen
February 3, 2011, 10:23 AM
I'll have to go look up it up in a reference book this evening.

BullfrogKen
February 3, 2011, 12:06 PM
Question: How much of a difference does adjusting the rear sight all the way left or right (relative to center) make on the target. IE how much does adjusting it full left move the impact point on a 25m zero target.

He claims (and i was pretty strongly disagreeing with) that anyone can pick up any rifle that has been 'properly zeroed' and fire fine w/ it (for the purposes of this discussion, land 5 out of 6 consecutive shots in the 'zero area' on an M4 / M16 25m zero target.

I'm pretty sure I'm in the right here, and all that really needs to be illustrated is the numbers: ideally i would posit that a weapons that's adjusted full left would cause someone who zeroed on a weapon that was adjusted full right to miss the black entirely, and have a way to explain why, and by (approximately) how much.

I thought about this for a while. You don't need to do the math and the equations to answer one of your questions.

If you want to see the effect of having the sights adjusted fully right or left . . .

The next time you have a rifle from the armory, find a safe area and set up your 25m zero target. Take the rifle with your known zero, set it in a stable rest, and sight in on the bullseye. Now have someone crank the sight all the way left or right. Acquire a new sight picture based on that new sight alignment. Assuming you have a steady rest, you'll see exactly how much you're now off your target with that large adjustment, and by how much you'd miss the mark.

As far as someone picking up a rifle with someone else's BZO and being close enough to make hits with it, he's probably right on that one. Different shooters can have their own sight adjustments based on their eyes and posture, but from what I saw it usually wasn't but a few clicks one way or another. But you can use that same method to test and see just how many windage clicks it takes to put you off target. Clamp the rifle down, sight it in on the target, and start moving the drum. See how many it takes until the sight picture takes you off your target.


That method's going to be a lot easier than having you take lots of precise measurements.

You'd need an accurate way of measuring:

your exact sight radius;
a precise set of calipers to measure how much one click of windage moves the sight;
then applying those measurements to a formula that measures the effect on a target at 25 meters.


If you still want the forumla I'll go look it up, but unless you know those first two figures it won't be of much use.

68wj
February 3, 2011, 12:42 PM
If your windage is maxed out to either side to BZO at 25m, there is a problem with that rifle or the shooter was not following the training.

The first part of that statement has little to do with your question, but the 2nd half says that your Plt Sgt is right (they usually are ;) ). The military teaches everyone, at least in their respective branch, to do things the same way. Same sight alignment, sight picture, sight manipulation, and BZO procedure. As long as each person did their part correctly, the next should be able to operate the other's weapon relatively the same. Increase your range to target and you will start to see more impact variance, but at 25m, or for combat accuracy needs, you should be fine grabbing a rifle off the deck and engaging.

henschman
February 3, 2011, 02:37 PM
It sounds like you and your platoon sgt. are talking about two separate things.

He is saying that anyone should be able to pick up a rifle that has been properly zeroed by someone else and hit the zero area of a 25m zeroing target without any further adjustment.

You are saying that if one guy's rifle is zeroed with the rear sight all the way left and you pick it up and move the rear sight all the way right, you will not hit paper. This is not the same as what he is saying, because if you moved the sights all the way right after the rifle has been zeroed, it will no longer be "properly zeroed," so there is no reason to expect a shooter to hit anything with it.

What your platoon sgt. is saying is true. As long as both shooters are getting proper sight alignment (with the top of the front sight post centered in the rear aperture) and are holding the sights in the same place on the target, they should be hitting the same place with the same rifle. The direction the sights are pointed and the direction the barrel is pointed do not change. The only thing that might change with a different shooter is that the two shooters might be putting the front post in different places in the aperture, or they use slightly different holds on the target... maybe one shooter's eyesight is blurrier than the other, and holds farther under the target for what he calls his 6 o'clock hold, etc.

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