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Redeyedrider
10-17-2015, 11:45 AM
When zeroing for 100m (at 25m)..... Where should the POI (point of impact) be on a 25m target to show a zero at 100m?

What I read is, "If you are trying to establish a 100m zero, your POI should be 1.5" below your POA (point of aim) at 25m".

This doesn't make sense to me because I would assume that the bullet will drop more over the 100m distance so logically you should have a POI higher than your POA at 25m.

Am I missing something?

Note: A2 Iron Sights

Don Nguyen
10-17-2015, 11:48 AM
Based on your figure, that would be assuming that the bullet has already reached its peaked height and isn't continuing to rise before hitting the target at 25m

Mossy Man
10-17-2015, 11:48 AM
i think you're missing gravity

frankm
10-17-2015, 11:52 AM
I had this saved in a file:

http://www.m4carbine.net/showthread.php?t=65679

Sight in with small aperture at 37/300 meters with the USMC BZO procedure,
which you can sight in at 25 meters with the 8/3 "z" setting,
then the small aperture will give a 50/200 zero automatically.

The small aperture is intended to be zeroed for a 300 meter zero
using M855 fired from a 20” barreled M16A2.

The 0-2 large aperture is intended to provide a 200 meter zero,
when the small aperture has been properly zeroed with M855 from
a 20” barreled M16A2.

If you examine the trajectories of M855 fired from a 20” barreled M16A2
zeroed at 300 meters, and at 200 meters, you will see that the
difference in elevation between these two trajectories (and hence the
difference in elevation between the small and large apertures) is 2.5 MOA.

Click Boom
10-17-2015, 11:59 AM
When zeroing for 100m (at 25m)..... Where should the POI (point of impact) be on a 25m target to show a zero at 100m?

What I read is, "If you are trying to establish a 100m zero, your POI should be 1.5" below your POA (point of aim) at 25m".

This doesn't make sense to me because I would assume that the bullet will drop more over the 100m distance so logically you should have a POI higher than your POA at 25m.

Am I missing something?

Note: A2 Iron Sights

yes, you are missing that with a 25m zero is angled upwards (the barrel) more in relation to the optical plane than a 100m zero.

a 25m zero POI is several inches higher at 100m than a 100m zero.

there are ballistic calc websites that can put it into more visual terms if that helps. google ballistic calculator.

Redeyedrider
10-17-2015, 12:05 PM
yes, you are missing that with a 25m zero is angled upwards (the barrel) more in relation to the optical plane than a 100m zero.

a 25m zero POI is several inches higher at 100m than a 100m zero.

there are ballistic calc websites that can put it into more visual terms if that helps. google ballistic calculator.

Now I think I get it. So basically the trajectory is still in the upward stage of the arc. So your 25m POI is at the early stage of that arc, hence hitting low....... I think

Click Boom
10-17-2015, 12:09 PM
here's what a 100m zero looks like.
http://gundata.org/ballistic-calculator/balcalc_chart_1445108754.png

So, if you bisected the trajectory line by putting a target at 25m, the bullet would hit roughly 1.5" low.

Redeyedrider
10-17-2015, 12:12 PM
You have cleared up my confusion.... Thank you! Great explanation.

Click Boom
10-17-2015, 12:15 PM
Here is a 25m zero. I generally dislike this zero as the bullet is like a foot high at 200m, and then harder to keep track of thereafter. Only makes sense for "aim at belt buckle 100% of time" infantry doctrine. I get hits to 3 and 400 just fine with a little kentucky windage on 100m zero.

http://gundata.org/ballistic-calculator/balcalc_chart_1445109202.png

Also, just fyi, if you play around with the ballistic calc on that site or others, your heigh over bore is 2.6" with an A2 sight.

Click Boom
10-17-2015, 12:26 PM
of course you could zero 1.5" low at 25m and be off 3" at 100m, you never really know until you do the far zero.

Redeyedrider
10-17-2015, 12:38 PM
of course you could zero 1.5" low at 25m and be off 3" at 100m, you never really know until you do the far zero.

Correct. Also variations in ammo. If I can get it dialed in close enough at 25m to within 3" at 100m, that should be a good starting point at the 100m mark. Thanks for your help.

PMACA_MFG
10-17-2015, 1:49 PM
Click Boom do you have the 50 yard zero?

Steve_In_29
10-17-2015, 6:37 PM
Unless you are shooting long distance there is info on the web explaining how a 50/200 yard zero is better as it keeps bullet drop to a minimum out to 300yds. My Saiga and my wife's SU16CA are both sighted in at 50/200yds and with the same POA (center of torso) will keep rounds in the torso of a man sized target from PB to 300yds. Both utilize an EOTech and 3x magnifier.

Cadre
10-17-2015, 9:20 PM
Zero at 25 shoot at 100 make adjustment .

Click Boom
10-17-2015, 10:30 PM
Click Boom do you have the 50 yard zero?

i usually use 50m for irons and 100m for optics

SocomM4
10-18-2015, 9:06 AM
I use a 50yd yero with POI 1.2 in below POA.

http://www.policeone.com/police-products/firearms/accessories/sights-scopes/articles/1298015-Sighting-choices-for-your-patrol-rifle/