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Old June 1, 2009, 11:25 AM   #1
BobNailer
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Zeroing my weapon question

I have a Bushmaster XM15 in 5.56mm with a Bushnell Holographic sight & flip up iron combat sights, I have a laser boresighter device, at what range would be best to zero my weapon's sights for relatively short-range urban combat? A lot of Iraq/Afghanistan veterans are out there who have experienced this firsthand, any advice on what the best range is?

Albert OConnor
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Old June 1, 2009, 11:31 AM   #2
zoomie
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25 yards
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Old June 1, 2009, 11:38 AM   #3
Brian Pfleuger
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I'd agree with roughly 25 yards but if you're shooting ONLY "relatively short range" the difference between a 25 yard zero and 100 yards zero is irrelevant. Somewhere between 17 and 30 yards is the optimum zero for maximum point blank range for almost every rifle ever made. Most are in the 21-27 yard range
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Old June 1, 2009, 05:41 PM   #4
AMX
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I prefer 50 yards. If you zero at 25 yards you'll hit high out to about 300 yards where the bullet once again crosses your point of aim. A 50 yard zero lets you aim at your target where you want to hit, instead of aiming low at 50, lower at 100, real low at 150, etc.

As an 11b, I had to zero at 25 meters with my M16 and did the same with my AR's for several years after I got out of the Army. After trying LTC. Chuck Santose's IBZ I'll never go back to 25 meters.
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Old June 2, 2009, 10:18 AM   #5
RangerHAAF
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If I recall correctly in my army days we zeroed our M16s at 25 yards and they were very accurate at long range; 300 meters(whatever that translates into).
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Old June 2, 2009, 02:27 PM   #6
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Can't you zero an AR for 25, and also be on at 200? Because of the distance of the sights above the bore, the bullet is travelling up as it crosses the 25yd line, then back down through the line again at 200. If you figure your target as a 6" circle, that's probably a 250yd point blank range. I shoot only at paper and steel, but I know guys who are shooting at 12" targets from 30 feet to 300 yards and not adjusting their sights.
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Old June 2, 2009, 05:15 PM   #7
AMX
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RickB- It's a 50 yard zero that = 200. A 25 yard zero = 300, give or take.
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Old June 2, 2009, 09:38 PM   #8
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I remember my dad had a chart with the "close range zero" for several calibers. Seems he used 27 yds for his .30-06 Springfield...his deer rifle. I don't know what happened to that chart. It gave the yardage for zero, plus, plus, zero, minus, minus for each cal listed. I wish I still had that chart.

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Old June 2, 2009, 10:25 PM   #9
Purity
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36 yards

We used 36 yard BZO in the corps. Here is the explanation from a USMC Weapons Training Battalion

"When a rifle is zeroed at 300 yards, the bullet will cross the line of sight twice. The bullet will cross the line of sight first on its upward path of the trajectory at 36 yards, and again farther down range at 300 yards (point of aim/point of impact). When the bullet’s trajectory intersects the line of sight at 36 yards and 300 yards, the rifle is considered to be zeroed to hit a target at the exact point of aim at both of these ranges. That is why there is an alternate, field expedient method for zeroing the rifle at 36 yards when a 300-yard range is not available. "
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Old June 2, 2009, 11:11 PM   #10
44 AMP
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may not stricly apply...

1975 Basic Training
M16A1
M193ball ammo
25meter "zero" (on special target, bullets struck below point of aim)
Spot on at 250 meters.
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Old June 3, 2009, 09:19 AM   #11
Bartholomew Roberts
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The military zeros at 25yds with the small aperture. This gives you a 300yd zero for the small aperture (about 5-6" high at 100yds) and then if you need to shoot under 200yds, you flip to the 0-200 aperture (the large, almost ghost-ring aperture), which is set to a different elevation.

The 50yd zero puts you within 2.6" of your line of sight from 0-225yds (roughly) and you should be dead on at 50yds and 200yds.

If you had A2 sights, the Santose 50yd zero lets you use the 50yd zero with the smaller aperture; but still use the elevation adjustments at longer ranges. However, most flip sights lack elevation adjustments and even those that do have elevation adjustments can't be adjusted like A2 sights to use the Santose zero.

For flip sights with no elevation, my preference is to use the 50yd zero with a same plane aperture (both apertures set for the same elevation). This lets me make hits to 300yds reliably, which is effective for my uses. This way I can use the small aperture for smaller targets close in (say 6" plates at 100yds) but still have a larger aperture for dusk/low-light conditions without changing my zero.

However, if you are just shooting at military style silhouettes (20"x42"), then the 25yd zero with different plane apertures makes good sense since it maximizes your point-blank distance.

Since holographic/red dot sights have no extra aperture, I always use the 50yd zero for these sights since it maximizes the effectiveness of these sights with a flat trajectory in the range they are best suited for (0-300m).

The 25yd zero for red dots doesn't really help with close-in shooting since below 25yds, the height over bore issue on ARs comes into play and you are talking 0.1" differences in point of impact between the 25yd and 50yd zero at distances under 25yds. At distances over 25yds, the 25yd zero for red dots is much more curved and less flat.
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Old June 3, 2009, 09:27 AM   #12
THEZACHARIAS
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The air force "Zeros" its M4s at 25yds, but the targets for the aimpoint have a "ghost outline" centered a few inches lower.

You use the black target as your point of aim, but you adjust your point of impact to the center of the ghost target. Basically, it immitates a 300yd zero without the 300yd range.
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Old June 3, 2009, 05:42 PM   #13
AMX
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I used the JBM ballistic calculator at www.eskimo.com to see the difference between a 25y zero, a 25 meter zero (Army), and a 50 yard zero.

The ammo is M193 .243 BC at 3,165fps.

.....25y.................50y ...................25m
25y....0.0.........25y......-1.2...........25m....0.0
50y....2.4.........50y........0.0...........50m....2.3
75y....4.5........75y.........0.9.............75m....4.3
100y..6.4......100y........1.6............100m...6.1
125y..7.9......125y........2.0............125m...7.4
150y...9.2......150y.......2.1............150m...8.4
175y.10.2......175y.......1.9............175m...9.0
200y..10.8.....200y.......1.3............200m...9.1
225y...11.0....225y........0.3............225m..8.8
250y...10.8.....250y.....-1.0............250m..7.9
275y...10.2......275y.....-2.8............275m..6.5
300y.... 9.1......300y......-5.1...........300m..4.5
325y.... 7.5.......325y.....-7.9............325m.1.8
350y.....5.3.......350y....-11.2...........350m-1.6

This is why I suggest 50 yard zero's on AR/M16's.

Edit- There, that's a little better.

Last edited by AMX; June 4, 2009 at 04:26 PM.
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Old June 3, 2009, 06:14 PM   #14
hogdogs
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Call me stupid if you wish but I didn't know a bullet had the aerodynamics to gain altitude. That would be pretty incredible.
I was under the impression that the perceived increase in altitude was actually the difference in elevation from muzzle to sight plane.
If so a AR with a handle mounted sight is far different than a single shot .22. so where to zero would change for most usable range with least amount of muzzle rise required...
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Old June 3, 2009, 07:03 PM   #15
ENC
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Brent you aren't stupid the bullet does not rise. It does nothing but drop as soon as it leaves the muzzle. But this is only true if the barrel is held exactly level or at a downward angle. Usually when we are aiming a rifle the barrel is pointing upward. This will make the bullet rise thus creating an arch for the bullets trajectory. Since line of sight is a straight line the bullet will cross the line of sight twice (usually).

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Old June 3, 2009, 07:59 PM   #16
hogdogs
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Okay, thanks, Evan... So the muzzle is upwards to the scope/sights view? Thus the "rise"?... that does clarify for me.... I zero my .22lr at 50 yards since my shots are 35-70 give or take so I just raise or lower just little for small game.
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Old June 3, 2009, 08:49 PM   #17
ENC
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So do I win a guided dog for hog hunt next time I'm in FL? LOL
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Old June 3, 2009, 08:53 PM   #18
hogdogs
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Sure! I offer everyone a free experience to try runnin' with the dogs... Gun hunts are tuff and I ain't that great as a guide... the hogs must be smarter than me
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Old June 3, 2009, 10:03 PM   #19
AMX
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Old June 8, 2009, 10:33 AM   #20
BobNailer
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Re: Zeroeing my weapon question redux

Thanks for all the info supplied, it really helps. I'll use my laser boresighter to co-witness my Holo sight and flip up iron combat sights together on a specific spot at 50 yds; co-witnessing so that if my holo sight craps-out, I can use iron sights as backup. You guys know a lot more about this stuff than me but I'm trying to learn. Thanks.

Albert O'Connor

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