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backbencher
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Posted: 8/22/2011 2:42:46 AM
Ok, behind the CHU, I have a sandbag point @ 25 M from the T-Wall. I am not an Infantry officer, I have a M4 w/ Aimpoint, flip down BUIS adjustable for windage & elevation 200-600 M, 14.5" bbl, and a Laserlyte bore sight. The ammunition is M855, and I need to reset to a 25m/300m zero. I've looked @ the charts in the FAQ, and read the instructions w/ the Laserlyte, but I'm not tracking where I should be zeroing.

Put the BUIS on 300, & spot on the laser dot @ 25M? Zero the Aimpoint to the dot @ 25M? Or should they both be below the dot by an inch or so?

I've read about the 200 M zero, but @ this time I'd prefer to stick to the bog-stock official Army way - albeit I don't have range time.

Farmers Fight!

backbencher
RedFalconBill
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Posted: 8/22/2011 11:46:04 AM
Unless you have a 6/3, or 8/3 rear sight, the 25M/300M two/one click zero method does not work as well as others.

At 25M, set your rear sight to '2' and then zero it so that your POI is 1" below your POA.

Confirm this zero by going out and shooting at 200M.

At 100 yds, this zero should be ~1.7"-1.8" high.
Nuke_Head
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Posted: 8/22/2011 12:26:25 PM
The reason why the US Armed Forces decides to use 25/300m sight-in/zero method is because M855/M856 have two(2) zeros. You can set the rear sight on the 300m mark and zero at 25m using the standard M-4 25m zeroing target. POA should be just at shoulder level on the silouet. POI should be about 1/2 to 3/4 inch lower. I guarantee you will be hitting targets like crazy. POI's @ 50m is about 3 inch high, @ 150m is about 1.5 inches high and @ 300m is about .5 inches low

Once you achieve this, all you have to do is centralize the red dot of the Aimpoint flushed with the front sight post throught the peep hole and you are done.
backbencher
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Posted: 8/22/2011 12:53:26 PM
Bill,

Are you saying set the PADS to 200, & set it 1" above the laser reflection @ 25m?

http://jtdistributing.net/store/product1605.html

How do I set the Aimpoint to a 300m zero then? We only have a 25m range here, & I doubt I'll get range time.

Farmers Fight!

backbencher
RedFalconBill
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Posted: 8/22/2011 1:01:06 PM

Originally Posted By Nuke_Head:
The reason why the US Armed Forces decides to use 25/300m sight-in/zero method is because M855/M856 have two(2) zeros. You can set the rear sight on the 300m mark and zero at 25m using the standard M-4 25m zeroing target. POA should be just at shoulder level on the silouet. POI should be about 1/2 to 3/4 inch lower. I guarantee you will be hitting targets like crazy. POI's @ 50m is about 3 inch high, @ 150m is about 1.5 inches high and @ 300m is about .5 inches low

Once you achieve this, all you have to do is centralize the red dot of the Aimpoint flushed with the front sight post throught the peep hole and you are done.

An M-4, firing M-855 ammo, with a 25M zero, and the rear sight set @ '3', the round will be ~1.5"-1.75" high @ 300M.

You are using book values and M-855 doesn't give 2,970fps out of ANY 14.5" barrel. This faster I've chrono'ed has been ~2,920fps, and most of it has been ~2,880-2,910fps.

I do not like an absolute co-witness, and tell people so, however I give people the choice between an absolute co-witness and a lower 1/3 co-witness.
RedFalconBill
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Posted: 8/22/2011 1:17:45 PM
[Last Edit: 8/22/2011 2:48:07 PM by RedFalconBill]

Originally Posted By backbencher:
Bill,

Are you saying set the PADS to 200, & set it 1" above the laser reflection @ 25m?

http://jtdistributing.net/store/product1605.html

How do I set the Aimpoint to a 300m zero then? We only have a 25m range here, & I doubt I'll get range time.

Farmers Fight!

backbencher

I would use a laser to get me on the paper, nothing more.

Yes, set the rear sight @ '2' and zero your carbine so your rounds impact 1 inch below your point of aim.

The PADS sight, by Matech, is better than a lot of people think, but do not tighten the locking screw too much, or you will snap the screw/clamp.

Unless I had the Matech adjustable base for the Aimpoint H-1/T-1, I would zero the same way.

Which Aimpoint are you using?

Not get range time? Why not? Without range time, you will not know if you need an extra click, or two, on the windage or elevation, when you fire live ammo.
Nuke_Head
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Posted: 8/22/2011 1:41:04 PM
[Last Edit: 8/22/2011 2:08:57 PM by Nuke_Head]
Originally Posted By RedFalconBill:

Originally Posted By Nuke_Head:
The reason why the US Armed Forces decides to use 25/300m sight-in/zero method is because M855/M856 have two(2) zeros. You can set the rear sight on the 300m mark and zero at 25m using the standard M-4 25m zeroing target. POA should be just at shoulder level on the silouet. POI should be about 1/2 to 3/4 inch lower. I guarantee you will be hitting targets like crazy. POI's @ 50m is about 3 inch high, @ 150m is about 1.5 inches high and @ 300m is about .5 inches low

Once you achieve this, all you have to do is centralize the red dot of the Aimpoint flushed with the front sight post throught the peep hole and you are done.

An M-4, firing M-855 ammo, with a 25M zero, and the rear sight set @ '3', the round will be ~1.5"-1.75" high @ 300M.

You are using book values and M-855 doesn't give 2,970fps out of ANY 14.5" barrel. This faster I've chrono'ed has been ~2,920fps, and most of it has been ~2,880-2,910fps.

I do not like an absolute co-witness, and tell people so, however I give people the choice between an absolute co-witness and a lower 1/3 co-witness.


That why I suggest that the POA should be at least .5 to .75 inches higher than the POI at 25m....

Yes you are right about the FPS on an M-4.....
if you don't like co-witness thats ok.....I just use it to explain new shooters how to set up Holo and RD using the irons.

I guess you are a seasoned shooter......may I suggest you to place the red dot 1 to 1.25 inches above the laser at 25m?


Edit:
I stand corrected ...the POI should be arround 1 to 1.25 inches lower at 25m with the POA at shoulder level....my bad for the confusion
backbencher
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Posted: 8/22/2011 2:23:13 PM
Range time (& ammo) tends to be reserved for folks going outside. My unit no longer owns the range, & I'm about to be orphaned. It's been 6 months since I shot last, & while the CompM4 was close, I could only get the PADS on the paper by cranking it up to 600m. My rifle went to reset after I zeroed before deployment.

So, I have built a laser zeroing range behind the CHU, but the POI will NOT be where the nice laser dot is @ 25m. So my question is not about POI, but how I should boresight. How much does the M855 drop out of a 14.5" bbl in 25m?

Farmers Fight!

backbencher
scottrh2
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Posted: 8/22/2011 4:07:45 PM
Have your read FM 3-22.9 starting at page 8-2 dealing with boresight zero? Page 8-6 deals with CCO boresight zero with the laser.
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RedFalconBill
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Posted: 8/22/2011 9:26:10 PM

Originally Posted By scottrh2:
Have your read FM 3-22.9 starting at page 8-2 dealing with boresight zero? Page 8-6 deals with CCO boresight zero with the laser.

I thought you used the borelight @ 10 Meters?

Need to go back and read Chapter 8.
backbencher
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Posted: 8/23/2011 1:03:03 AM
Ah, much thanks. Just move the sandbags 15m, print the right target, mark the right offsets, ignore the bit about using the super-accurate boresighting laser the Army hasn't issued, sandbag it so it won't move, and Bob's my uncle.
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Posted: 8/23/2011 12:58:16 PM
Sigh. Printed the right target from the PDF, but my settings were off - my little squares are not 1cm. And even if they were 1cm, I'm still confused. For a 300m zero, what is the relationship between the Laserlyte dot & the Aimpoint dot at 10m or 25m?

Working through the Oehler Ballistic Explorer tutorial right now, wondering if I ever figure out the program if it will give me the answer I seek : )

FF!

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scottrh2
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Posted: 8/23/2011 9:55:54 PM
You are making this way too hard. Reduced range zero is to speed up your zero process. Prior to departing a FOB and going hot you need to at least shoot it at 25m and zero your BIS and CCO. I know it is a PITA to gear up with the IOTV and crap just to do a zero but you need to get it done.
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Posted: 8/24/2011 2:12:34 AM
I'm never going outside the wire. That's not my job. It would be nice, but the closest I get is to pedal the bike all the way around the perimeter. Ergo, no range time, no ammo for me. I'm not sure how else I can explain this. It would be nice to walk over to the range, and say, hey, I'd like to zero my rifle, but that's not how things work these days.
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Posted: 8/24/2011 8:40:26 AM
Originally Posted By backbencher:
I'm never going outside the wire. That's not my job. It would be nice, but the closest I get is to pedal the bike all the way around the perimeter. Ergo, no range time, no ammo for me. I'm not sure how else I can explain this. It would be nice to walk over to the range, and say, hey, I'd like to zero my rifle, but that's not how things work these days.



LOL! Hell I would turn it in to the armory and get a pistol if I had to carry something to the DFAC. I will be in Kuwait before the end of the year and other than "troop morale visits" I will be in your same situation.

"Of the Troops, For the Troops"
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backbencher
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Posted: 8/24/2011 9:10:07 AM
Well, I'm hoping to draw a pistol as well, for these last few months, just in case. But back to the original question - on a laser range of 25m or shorter, what should the relationship be between the laser dot, the BUIS, & the Aimpoint dot to produce, as closely as possible, a 25/300m zero, given an M4 w/ 14.5" bbl, & M855 ammo?
RedFalconBill
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Posted: 8/24/2011 11:41:12 AM

Originally Posted By backbencher:
How much does the M855 drop out of a 14.5" bbl in 25m?

backbencher

The M855 drop is ~0.3".

Originally Posted By backbencher:
Well, I'm hoping to draw a pistol as well, for these last few months, just in case. But back to the original question - on a laser range of 25m or shorter, what should the relationship be between the laser dot, the BUIS, & the Aimpoint dot to produce, as closely as possible, a 25/300m zero, given an M4 w/ 14.5" bbl, & M855 ammo?

You have used the term Laserlyte more than once. Can I take this to mean that you are not using the Insight LBS, but you are using the Laserlyte brand boresight device?

If this is the case, I would go back to what I said earlier, set the BUIS to '2' and adjust the laser's POI to be 1" below your POA, @ 25M. Once this is done, you can use the lever to adjust your range from 200M through 600M.

With the Aimpoint, to quickest way is to use an absolute co-witness and adjust the dot until it is on the tip of the front sight.

Still not comfortable with a SM using a carbine w/o a confirmed zero, but then I'm a curmudgeon.
backbencher
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Posted: 8/24/2011 4:19:59 PM
Bill,

I'm not comfortable w/ it either, but I'd rather an unconfirmed zero when on walk-about on the COB, than a known-bad zero. Just my preference.

Ok, let me see if I have this straight. Set the Matech on 200m. Sight it in 1" above the laser dot @ 25m. That I can do.

Then, set the Matech on 300m. Without the bore laser, just adjust the Aimpoint so the dot is just above the front sight, clearly visible in the rear aperture of the Matech BUIS.

Or is the Aggie still confused?

FF!

backbencher
RedFalconBill
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Posted: 8/25/2011 9:53:29 AM

Originally Posted By backbencher:

Then, set the Matech on 300m. Without the bore laser, just adjust the Aimpoint so the dot is just above the front sight, clearly visible in the rear aperture of the Matech BUIS.

Using your irons to set your M68 should be enough to get you close.

Be consistent with your cheek weld.
backbencher
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Posted: 10/1/2011 8:11:30 PM
All:

I did try to zero the rifle w/ the laser, but alas, I can't see the difference btwn the dot & the 1"dot above @ 25 yards through the Aimpoint. An alternate solution: calculate the coincidence point of the boresight line and the line of sight. This has the added convenience that the weapon need not be sandbagged as securely, as well as providing different ranges for any weapon for which the trajectory can be calculated, from hunting bullets in .30-06 to 40mm HE in the M203.

The formula is B=(I*H)/R, where:

H is the height above center of bore of the center of the rear sight aperture
R is the rise of the bullet in the 1st increment of the calculated trajectory
I is the distance of the 1st increment of the trajectory from the muzzle
B is the distance where the boresight and the line of sight are coincident.

Using the following assumptions:

M4 BUIS sight height set to 300m - 2.6" (may change on receipt of further information)
A G7 BC of .154 from Applied Ballistics for Long-Range Shooting, by Bryan Litz
A bullet weight of 62 gn from the NATO specification
A MV of 2900 fps (may change on receipt of further information)
A 300m zero from Army doctrine
The ballistics calculator @ http://www.jbmballistics.com, using 1m increments.

We get a boresight range of 28.43389 yards, or 26m, given the above assumptions. It looks like JBM's calculator gives the bore angle as well, which would add to the accuracy of this calculation. An alternate calculation, then, would be B=H/TanA.

Farmers Fight!

backbencher
scottrh2
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Posted: 10/1/2011 10:47:16 PM
30 days later and you are still trying to get this M4 zeroed? Hell when does the rotation end?
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Posted: 10/2/2011 12:07:28 AM
This place is actually good for my allergies. I've extended to become a retrograde SME.

Farmers Fight!

backbencher