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Posted: 9/15/2004 8:28:19 AM EST
I zeroed my Larue BUIS today. Got a spectacular zero at 25 meters. When I pushed the target out to 50 meters my shot were all hitting about 3 - 4 inches too high.

I'm using XM193 throught a 14.5 inch 1/9 twist barrel.

Is this what is supposed to happen or am I doing something "wrong?"

Thanks
Link Posted: 9/15/2004 8:31:54 AM EST
You're a whole lot better off zero'ing at 50 yards. Then you'll be +/- 2.5" from 10 yards out to about 225 yards.

Luck,

SD
Link Posted: 9/15/2004 8:44:58 AM EST
The Marines are now zeroing their weapons at 36 yards. Even the old 25m zero method (which has been shown to shoot too high) required adjusting the elevation wheel before shooting.

Zeroing at 50 yards, as SailorDude suggests, produces a very flat trajectory while still providing adequate range.
Link Posted: 9/15/2004 9:25:15 AM EST
You are doing it right. The military does 25 yard zero's because they've ALWAYS done 25 yard zeros, not because its the best way to do it.

Read up. You may find the 50 yard zero is the zero for you.
Link Posted: 9/15/2004 9:40:18 AM EST
For info and details on the 50 yard / 200 meter zero, from the Maryland AR-15 Shooter Site:

An Improved Battlesight Zero by Lt. Colonel Chuck Santose.
Link Posted: 9/15/2004 9:53:50 AM EST
It should be high.

Where you sight in does not affect trajectory (the trajectory is what it is). The distance to the initial intersection of the sight axis and trajectory will what the battlesight range is though. Sight in at 50 yd as suggested by others and your good to go to up to about 270 m.
Link Posted: 9/15/2004 10:27:03 AM EST
As you can see by these graphs of a 223 zeroed at 25 yards, it is doing what it is supposed to do:


Link Posted: 9/15/2004 10:32:55 AM EST
Just to further the information, here is a 36 yard zero:



and a 50 yard zero:



Just remember, that it will vary by ammo.
Link Posted: 9/15/2004 10:34:54 AM EST
[Last Edit: 9/15/2004 10:36:59 AM EST by spookyspiff]
Excellent graph. Can you point me to the same thing for a 50 YRD zero? THanks for all the responses.

edited to add: wow excellent. thanks.
Link Posted: 9/15/2004 10:40:31 AM EST
Link Posted: 9/15/2004 2:27:08 PM EST
[Last Edit: 9/15/2004 2:28:40 PM EST by spookyspiff]
Could anyone explain why it is that when the rifle is zeroed at different ranges that the rise and fall in inches at other distances is different between the different zero ranges?

Here's what I mean:

At 25 yard zero, the strike of the round varies by 8 inches or more at less than 200 yards.
With the 50 yard zero, the strike of the round only varies by a couple inches no matter the distance of the target.

I think I know what's going on here, but doesn't this almost sound like the round is "shooting flatter" for the 50 yard zero?

[I believe what's happening is that with the 25 meter zero the rifle is firing at slightly higher upward angle. or maybe i'm clueless here.]
Link Posted: 9/15/2004 2:33:37 PM EST

Originally Posted By spookyspiff:
Could anyone explain why it is that when the rifle is zeroed at different ranges that the rise and fall in inches at other distances is different between the different zero ranges?

Here's what I mean:

At 25 yard zero, the strike of the round varies by 8 inches or more at less than 200 yards.
With the 50 yard zero, the strike of the round only varies by a couple inches no matter the distance of the target.

I think I know what's going on here, but doesn't this almost sound like the round is "shooting flatter" for the 50 yard zero?

[I believe what's happening is that with the 25 meter zero the rifle is firing at slightly higher upward angle. or maybe i'm clueless here.]



Yes with a 50yd zero you're giving less cant to the barrel hence the bullet won't climb as high.
Link Posted: 9/15/2004 2:41:38 PM EST
Yes, at 25 yds, the angle is greater. You are at a completely different point on the curve.

The 50 yd zero takes the greatest advantage of the ballistic curve to acceptable +/- variance at practical ranges.

Why adjust the sights to obtain zero at 375 yd, when it makes you shoot 10"-11" high at 150-250 yd??? That is stupid. You have adjusted your rifle to shoot over the target at ranges where you are likely to shoot.

Now look at the 50 yd zero. +/- 2.5" out to 260 yds is excellent.

This is a no brainer.
Link Posted: 9/15/2004 3:21:20 PM EST
If you don't normally have access to a 50yd range, and I read the charts correctly, you should be able zero about 1" low at 25yds. Someone please correct me if I am wrong.
Link Posted: 9/15/2004 4:39:57 PM EST
Simply put, you are matching your line of sight with the arc of the bullets travel. That arc is going to be constant. If you compare to a 25 and 50 yard sight, the bullet arc meets the line of sigth at a higher angle at 25. This means that the bullet will rise higher above the line of sight and recross it sooner. With the 50 yard sight they cross farther away and the arc doesn't rise as far above the line of sigth.

For a graphic example do this. Fold a sheet of paper in half lengthwise. Fold it in half again. Unfold it and draw an arc (doesn't have to be exact) in the middle 2 quarters. Now take a second sheet. Make two marks on the top edge, about 1 1/2 and 3 inches from the left end. Now, put the left corner of that sheet about 1/2inch above the left end of the arc and pivot the paper on this point. Line up the first mark (represents 25 yard zero) on the arc and make a mark wher the arc recrosses the edge of the second sheet. Measure how high the arc is above the edge of the second sheet at its highest point. Now do the same thing with the second arc, the second mark represent the 50 yard zero.

Even though the arc is constant, those intersection points change percetibly and the distance between the arc (bullet path) and the edge of the paper (line of sight) change considerably. Your paper was covering the bottom end of the arc, but it changed similarly. This is in no way accurate to the results you will see with the actual thing, but it gives you the idea.
Link Posted: 9/15/2004 5:00:48 PM EST
[Last Edit: 9/15/2004 5:07:38 PM EST by spookyspiff]
this is really great info. Next time I go to zero with the Army I'll be sure to explain all this and ask to set up 25 meters behind the firing line.

Har har.



[edited to add: Of course, I WILL be zeroing at 50 meters next time at the civy range]
Link Posted: 9/15/2004 7:33:05 PM EST
Yes, if you MUST "zero" with a 25 yd target, group should be 1" below point of aim.

If you can check at 100 yds, your group should be centered 1.75"-2" above point of aim.
Link Posted: 9/16/2004 8:36:40 PM EST

Originally Posted By Lumpy196:

Originally Posted By SailorDude:
You're a whole lot better off zero'ing at 50 yards. Then you'll be +/- 2.5" from 10 yards out to about 225 yards.

Luck,

SD



+1000



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