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25 yd. zero related to a battle sight zero - copied from old forum

Started by Old Dog, June 25, 2007, 07:45:24 PM

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Old Dog

June 25, 2007, 07:45:24 PM
wildman
RevWarVetAssoc Staff
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Posts: 235

     Zero?
<< on: July 8, 2005, 02:17:00 PM >> Quote 

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I have in my hand a hand out from one of the rifle clinics. It's the one with the six steps of firing plus 25 meter drill targets. At the bottom are the following zero instructions. "From 25 meters, with your sights 2 MOA above POA," Following these instructions produces a zero at what yadage? My guess is 150 yards. the next line reads to ,"get your 200 yard zero, come up 1 MOA.
There are 2 MOA built into the sights of an M1 between 100yrds. and 200yrds. I assume the M1A is the same.  That's the question, at 25 yards if ones bullet hits 2 MOA above POA at what yardage is one zeroed?

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This is my rifle. There are many like it but this one is mine.... "My Rifle" the creed of a US Marine by MG WH Rupertus,USMC


Mike in NC
Regular Poster

Posts: 94

Live Free or Die

     Re:Zero?
<< Reply #1 on: July 9, 2005, 08:40:13 PM >> Quote 

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If you are zeroed at 25m, that gives you a 200 yard zero.  Then if you come up 2 MOA (1/2" at 25 yds.), you will be at your battle sight zero (BSZ) for 275 yards (250m).

Mike

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"Those who expect to reap the blessings of freedom must, like men, undergo the fatigue of supporting it."  Thomas Paine
 
Spartacus2002
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Posts: 649

Rifleman & instructor

     Re:Zero?
<< Reply #2 on: July 10, 2005, 09:05:47 AM >> Quote 

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the battlesight zero allows hits on a target out to 300 meters/yards while aiming at the center of the target.  It will be a little high at 100 and 200 yards and a little low at 300 yards.

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I love the man that can smile in trouble, that can gather strength from distress, and grow brave by
reflection. 'Tis the business of little minds to shrink, but he whose heart is firm, and whose
conscience approves his conduct, will pursue his principles unto death.
--Thomas Paine (1737-1809)
 
fred
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Posts: 1285

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      Re:Zero?
<< Reply #3 on: July 10, 2005, 12:03:45 PM >> Quote 

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Wildman - Twenty-eight views (as this is written), and only Mike in NC has stepped up to the plate to fire back with an answer (the textbook one, always a good one to give), along with Spartacus, and it's not surprising, as before we go too far, you're gonna need to strap on your hip boots, as we're gonna wade way out in the swamp.

    Generally speaking, a POA [Point-of-Aim] zero at 25M is gonna be pretty much a POA zero at 200 with the military calibers most of us fire. (You may have to add or drop a click or two for your rifle, but you?re in the ball park, for sure.)

    [And to deal with another issue you raise, the 'come-up' for 30-06 from 100 to 200 yards is generally listed as 2.5 MOA. Because there are no half-minute clicks on the M1 rear sight, some one in the sight development stage rounded it down to two clicks, which is why you have two clicks from 100 to 200 on the sight. They could as easily have rounded it UP to three... but this really has nothing to do with your base question.]

    Now, to start wading, let's understand that most shooters choose one of two 'holds' on the target.

    One is the standard six-o'clock, where you put the front sight on the bottom of the target, having previously adjusted your sights so the bullet will strike COT [center-of-target].

    The other is the 'center hold', where your front sight is placed on the center of the target.

    Prob over 90% of the shots fired by target shooters (not plinkers) are aimed six o'clock, because it provides a very definite aiming point, and the distances being standard, it is easy to adjust your sights to hit COT.

    With a center-hold, your black front sight on a black target does not make - for most people - the kind of definite AP [aiming point] you need.

    But with center-hold, your sights are not 'off' - they are adjusted so that the shot falls right where they [the sights] are placed.

    So we have a hold where your shot is adjusted to hit higher than your AP, and another where the shot hits the AP.

    So far, so good.

     Now, what happens when target size changes? Say the bull is smaller?

    Or the bull stays the same, but is farther away, so its size in MOA is less?

    So if a bull is 4 MOA at 300 yards, and you hold six o'clock, your sights have to be 2 MOA above POA for the bullet to hit the center of the target, right?

    Move that same bull out to 600 yards.

    Standard comeups say from 300 you add 7 clicks (MOA) to be 'on' at 600.

    But the bull, while its actual size has not changed, is now only 2 MOA, and your sights if adjusted by the manual would be 2 MOA above POA, and your shot - if you are lucky - might clip the very top of the target, not the center. Or be an outright miss.

    You would need, in this example to come up one click LESS than the manual to adjust for the bull ?shrinking? 2 MOA.

     In other words, the target size in MOA has to be factored in with a six o'clock hold. So instead of raising your sight 7 clicks, you'd only raise 'em 6.

    None of this is a problem on the target range because the standard bulls used in competition get larger as the range increases - plus you are given sighter shots - so sight adjustment is not an issue.

    Simple, so far, right?

    Now, what about field shooting? At indistinct targets at guesstimated ranges.

     Now, my friend, the rubber is about to meet the road.

    You can argue six o'clock is the right hold, as the target, already hard to see, is not half obscured by the front sight, as a center hold would do. At long distances, that target can get mighty small.

    On the other hand, keeping track of target size in MOA while adjusting sights under pressure would be tough, favoring the simplicity of aiming COT.

    I'll tell you what I do on the RWVA range, with man-sized and -shaped targets that sometimes can be pretty indistinct, even if range is known precisely.

    I add 2 MOA to my 200 yard sight setting, to get a battlesight zero of an official 275 yards (250 meters), like the book says. [Yet another 'fudge', as in real life going up two clicks between 200 and 300 mathematically puts you at 266.67 yards and ballistically, prob at 269-270 yards, not the perfect 275, but we're deep enough in the swamp already....]

    With that sight setting, I aim 6 o'clock at 200, and the bullet skims 4" over the  berm in front of the target to knock the target down. Sure thing, every time...

    At 300, I aim COT, or maybe even a little higher, and the target will drop.

    At 400, I raise the sights to 400, and aim COT.

    At 500, I raise the sights to 500, and aim COT.

     Usually, you are under some time pressure at RWVA, so you don't have time to 'fuss around' with sight adjustment. But even keeping it simple, it?s best to mark your battle-sight zero with nail polish so you can quickly come back to it.

    Out in the field would not be a lot different from the above.

     Anything out to 300 would be 'dead-on', tho I would mentally make the adjustment of aiming 6 on nearer targets, and COT on those shrinking close to the width of the front sight blade (ie, getting near 300 yards).

    Those targets less than front sight blade in width (more than 300 yards away) would see a sight adjustment or, if time did not permit, a rapid shot holding above the target (over the head at 400, half target high at 500).

    A low miss is far better than a high one. A ricochet can hurt a lot and counts as a ?hit?, whereas a 'crack' overhead has moral value only. (So estimate range max and min, and favor the minimum side.)

     Say, how?s that for swamp work? Not so bad, was it?

    And we didn?t even get into discussing front sight color and its potential effect on sight picture. (What, think just because you blacken your sight for the target shoot, that?s gonna be the best thing if the balloon ever goes up? Might want to think again...)

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wildman
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Posts: 235

     Re:Zero?
<< Reply #4 on: July 11, 2005, 10:00:39 AM >> Quote 

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Thanks for the input.

Remember the orginal question. If my bullet hits 2MOA above POA at what yardage am I zeroed?

What I am trying to fiqure out is why at the RWVA event I was wacking 400 and 500 yd pop-ups but did poorly at 200 yds. Unfortunetly neither I nor the spotter could see the bullet splash.

I belive I would do better at the closer ranges 300 or less if I could zero to hit point of aim. 

What I need to do is shoot more.

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This is my rifle. There are many like it but this one is mine.... "My Rifle" the creed of a US Marine by MG WH Rupertus,USMC
 
cabinboy
Guest
  Re:Zero?
<< Reply #5 on: July 12, 2005, 09:24:23 PM >> Quote 

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Mebbe we can get some bulls at 200 yard so that we can see where the 25m zero actually hits....

Spartacus2002
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Posts: 649

Rifleman & instructor

     Re: Zero?
<< Reply #6 on: October 28, 2005, 11:53:44 PM >> Quote 

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I have learned that a 25 meter zero for my rifle is about two MOA too high for a true 200 meter zero.  I practice at 25 meters but confirm my 100 yard zero.

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I love the man that can smile in trouble, that can gather strength from distress, and grow brave by
reflection. 'Tis the business of little minds to shrink, but he whose heart is firm, and whose
conscience approves his conduct, will pursue his principles unto death.
--Thomas Paine (1737-1809)


"The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter cannot be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles."

—Jeff Cooper, The Art of the Rifle
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