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Zeroing the M4 and AR-15:


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#1 OFFLINE   Quentin

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Posted Nov. 17 2009 - 01:18 PM

As a new owner of an AR I've been soaking up as much information as I can find about it and am surprised how much misinformation is out there on basic sight zeroing, even from manufacturers. To figure out the best zeroing schemes I pulled together the best of the best that I can find into the following document - and thought it might be useful to others.

I thought I'd put it up here as a straw man and let you guys who know more on the subject and are interested throw rocks at it and knock it down - and hopefully we can make it better. This is not a thread pitting iron sights vs. optics, the real issue is ballistics and sighting in. We all choose what's best for us but still all share the problem of getting POA to equal POI at various distances.

Would appreciate any comments and I hope this thread and its replies end up shedding more light on the subject! Thanks!



Zeroing the M4 and AR-15:
Taking Full Advantage of Carry Handle Sights


Getting your AR-15 on target at various distances can be a mystery since there are many zeroing schemes in use and many variations of the rifle. Then add in different barrel lengths which perform different ballistically, the wide range of ammo, and just what distance is best to zero for in the first place. Also, developing fundamental shooting and sighting skills takes dedication, effort and good eyesight. On top of that there is so much misinformation it’s hard to wade through all the crap to find what works best for you. Even manuals that come with rifles often are wrong! No wonder many AR owners give up on iron sights and go to optics thinking that will solve the problem, but technology also has difficulty solving all the problems of staying close to the bullseye at multiple distances.

Another problem is there are several versions of the carry handle rear sight that operate differently yet formal instruction tends to be given for one type, usually the A2 fixed unit found on the M16A2 and AR-15s based on this 20" rifle. However, most ARs sold today are M4 flat top carbines with a 14.5" or 16" barrel and often come with the A4 (M16A4) removable carry handle. When I bought an M4 style carbine and A4 (usually called A3) carry handle, I found it surprising how difficult it was to find correct information on operating the basic sighting system of such a popular choice. And that’s a shame since, even if it soon gets replaced with an optic, the A4 carry handle is a flexible sighting device (especially with modifications described below) that should be better understood. Good optics have important advantages such as quick target acquisition but if you have an unused carry handle it’s well worth investing some time and ammo to discover how useful it really can be. Also chopped carry handles work well in a back up role with many optics, especially red dot sights.

The path to unraveling the mystery begins with understanding the trajectory of the 5.56mm bullet in flight from the rifle's muzzle until it impacts a target. When you aim the rifle sights at a target, the line of sight is a straight line through the rear sight aperture, over the front sight post then straight out to the target. This is known as Point of Aim (POA). However much like a 50-yard football pass, the bullet travels in an arc, not a straight line, and wherever it hits is known as Point of Impact (POI). The trick is to get the straight line POA to equal the POI on that arc - and have it happen dead center on your target. At the muzzle the bullet is about 2.5" below POA because the sights are about that much higher than the centerline of the barrel. But the bullet soon rises above POA then downrange it falls back below POA. Depending on the rifle's initial angle of elevation you can expect a bullet to crossover the POA twice, once around 25-45 meters as it rises above POA and again around 200-300 meters out as it falls back to earth. Ballistics of 5.56mm bullets are well understood and the arc or trajectory is consistent if the rifle and ammunition and rifleman are all up to par. Understanding the bullet trajectory allows you to zero in the rifle at the closer crossover point (where POA = POI) and expect that the second crossover point also will be in zero, again POA = POI. The advantage is you zero at a shorter range, even a pistol range, with confidence that your long range zero will be true as well. Still, check that long range crossover on a day when the wind is calm.

Two popular zeroing methodologies are covered here - the US Armed Forces 300-Meter Battlesight Zero and the Santose Improved Battlesight Zero. We'll start with the 300-meter Battlesight Zero first because it's quite easy and is tailored for the M16/AR-15 carry handle with no esoteric adjustments. This is the method that's in general use by the US military while the Santose method hasn't been officially endorsed by the US Armed Forces at large but is gaining ground in and out of the military.

Battlesight Zero (BZ) is a handy method to get a military 300 meter zero at a 25 meter range (easier to find than a 300 meter range) because of the fortunate coincidence that the M4's crossovers are 25 and 300 meters. Get a good zero for 25 and you should be good to go for 300 meters as well. (See the second paragraph below for how the 20" rifle is zeroed at 25 meters.) BZ is described in detail in the M16 Operators Manual TM 9-1005-319-10 but let’s cut to the chase here.

Flip up the small aperture on the rear peep sight so it is used for sighting. Then set the M4 carry handle elevation knob to 6/3. Using 62 grain M855 FMJ and the targets linked below, fire groups of three shots and check the target after each group. To adjust bullet strike or POI left or right, use the windage knob on the right side of the rear sight. To adjust for elevation, leave the rear elevation at 6/3 and adjust the front sight post up or down. When shot groups are satisfactory at 25 meters, the M4 is successfully zeroed. To hit targets beyond 300 meters, turn the elevation knob clockwise to 4 for 400 meters, 5 for 500 and 6/3 (one full rotation) for 600. Return it down to 6/3 for normal range.

An AR-15 with a 20" barrel is battlesight zeroed differently because its first crossover is farther out, about 31 meters. Because of that, the A4 elevation knob is turned two clicks clockwise to the small 'z' mark before zeroing at 25 meters. After zeroing, move it back to 6/3 and the rifle is zeroed for 300 meters. For rifles with the A2 fixed carry handle marked 8/3, the knob has coarser adjustments where one click equals two on the 6/3 sight. So to zero a 20" rifle with A2 sights at 25 meters click the elevation knob one click clockwise instead of two. After zeroing move it back to 8/3 and the rifle is zeroed for 300 meters. AR-15 rifles with M16 or M16A1 sights do not have an elevation knob but can be "zeroed" about an inch low at 25 meters to achieve a 300 meter zero.

Links for more information:
http://www.armystudy...6a2-rifle.shtml Battlesight Zeroing the M16A2 rifle (for the M4, remember to zero at 6/3)
http://ohmr.ohio.gov.../ohmr2444-b.pdf Download Free M4 25/300 meter zeroing targets
http://www.bobdbob.c...a2-25m-zero.pdf Download Free M16 25/300 meter targets
http://www.usaac.arm...M16-M4 data.pdf US Army Rifle Marksmanship PDF with bullet path tables and graphs of the M4 carbine and M16 rifle

Looking at the 300m tables and graphs in the US Army Rifle Marksmanship PDF it's clear that between 50 and 275 meters the M4 and M16 shoot quite high - up to 7" high at 175 meters. And since the elevation knob is already cranked all the way down, there's no easy way to get the sight lower. The military does train holding the sights under the target and flipping the sight to the larger aperture that's marked 0-2, both of which bring down the point of impact. Unfortunately both techniques work with varying degrees of success depending mainly on the skill of the rifleman.

The deficiencies of the 300m battlesight zero at midranges lead us to the second zeroing scheme The Santose Improved Battlesight Zero (IBZ) which takes full advantage of the flat shooting 5.56 when zeroed at 50y/200m. Popularized by Lieutenant Colonel Chuck Santose, US Army (ret.), this ingenious technique involves modifying the A4 carry handle so the elevation knob bottoms out 4 clicks below the 6/3 setting. (The A2 fixed carry handle is set 2 clicks below 8/3.) To perform the modification, use a 1/16" Allen wrench to loosen a set screw so the elevation knob's top and bottom move independently. Turn the bottom ring four clicks clockwise making sure the sight post rises but 6/3 remains stationary and aligned with the index mark above it. Tighten the set screw firmly and turn the knob counterclockwise making sure that you can go four clicks below 6/3 (6/3 -4) then zero at 50 yards. Or click up to 6/3 and zero at 25 meters as described above in the BZ method. Since the rear sight has been raised, the front sight must be raised the same amount when zeroed. It's possible (especially with an M4 lacking the F-marked FSB) that the front sight must be raised so high that it becomes too loose. In that case Bushmaster's 0.040" taller sight post should solve the problem and only costs about $6. http://www.bushmaste...ucts.asp?cat=21

Once the M4 is zeroed in you can click below 6/3 four clicks to have the IBZ ranging scheme thatís within an outstanding 2.5" of line of sight from 0 to 230 meters! Thatís worth repeating - POI is within 2.5" of POA from 0-230 meters! (Of course that assumes you do your part of the job.) There is an enhanced version of the IBZ known as the Revised Improved Battlesight Zero (RIBZ) where the elevation knob is modified 6 clicks below 6/3, putting the M4 or M16A4 dead on at 100 yards. (For A2 sights go 3 clicks below 8/3.) In addition to 6/3 -6 for 100 and 150 yards, click to 6/3 -4 for the flat trajectory of the IBZ with zeroes at 50 yards and 200 meters, or 6/3 for standard BZ 25/300 meter zeroes including A4 ranging for 400, 500 and 600 meters. (My M4 did need a taller front sight post which had to be screwed deep in the well so I set the rear sight to bottom out 10 clicks below 6/3 which brought up both sights to a suitable level.) The RIBZ allows a quick click of the elevation knob for zeroes at most standard ranges found in the US: 25, 50, 100 and 150 yards plus military ranges too. Don't expect precision zeroing at every distance but it is astonishing how well this works. Definitely read the links provided for more information on these modifications. At first it looks daunting but actually is very easy to accomplish.

With the RIBZ modification an M4 should be on target if the elevation knob is set to the following:
Distance/Setting (y =yards/m=meters; up to 100 meters the difference doesn't greatly affect POI)
25m: 6/3
50y: 6/3 -4 (for the 20" A4 rifle; the M4 carbine will zero at 41 meters/45 yards)
100y: 6/3 -6
150y: 6/3 -6
200m: 6/3 -4
300m: 6/3
400m: 4
500m: 5
600m: 6/3 (after one full rotation upward)

http://grburnett.us/...lesightZero.pdf the Improved Battlesight Zero
http://www.m4carbine...thread.php?t=22 more about the Improved Battlesight Zero
http://www.ar15.com/...&...18&t=328143 more about the RIBZ

Consider the advantages of zeroing your BUIS and optics or even the old A1 carry handle with the Santose Improved Battlesight Zero. Though you won't have the handy elevation knob to make quick changes, you'll still gain the IBZ's flat trajectory from 0 to 230 meters. Think about that, set it and forget it - POI is within 2.5" of POA from 0 to 230 meters! Just zero in at the first crossover for your barrel length using the US Army Rifle Marksmanship PDF (200m table) or zero one inch low at 25 meters. (Remember Bushmaster's tall sight post if your front post gets too loose when you raise it.)

Bushmaster carry handle adjusted so it will go 10 clicks below 6/3
Posted Image


ArmaLite gas block front sight base with the 0.040" taller Bushmaster post
Posted Image

Edited by Quentin, Dec. 08 2009 - 04:21 PM.



#2 OFFLINE   Quentin

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Posted Nov. 17 2009 - 05:21 PM

Of course thanks must be given to Colonel Santose for his brilliant work on IBZ and Molon for the RIBZ revision. And thanks to those hosting free zeroing targets, the US Army for their links above, Greg Burnett for hosting the IBZ PDF and to the other AR sites for the threads linked.

Again this thread just pieces together the best of the best!

Edited by Quentin, Nov. 17 2009 - 05:24 PM.



#3 OFFLINE   slowrider

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Posted Nov. 17 2009 - 05:56 PM

I'm still new to the AR15 seen. But I'd like to say great job on this writeup :thumb:


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#4 OFFLINE   Quentin

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Posted Nov. 17 2009 - 06:22 PM

Thanks, SlowRider! One of the problems I had was so much excellent information was out there but it was written for different versions of the equipment I had - so figured I'd distill it down to what worked with my M4. I think it's right but hope to get feedback to verify.


Say, we both have 101 posts!


#5 OFFLINE   slowrider

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Posted Nov. 17 2009 - 07:20 PM

Thanks, SlowRider! One of the problems I had was so much excellent information was out there but it was written for different versions of the equipment I had - so figured I'd distill it down to what worked with my M4. I think it's right but hope to get feedback to verify.


Say, we both have 101 posts!

I have a Bushmaster XM15 E2S 16" flat top carbine with A3 removable carry handle(that's what the manual called it) and believe it or not the manual that came with it says to zeroing your sights basically like you said

Because of that, the A4 elevation knob is turned two clicks clockwise to the small 'z' mark before zeroing at 25 meters. After zeroing, move it back to 6/3 and the rifle is zeroed for 300 meters


And when I set my sights back to 6/3 and shoot at 25m the sights are dead on, unfortunately I've not had the chance to shoot any further than that yet.


#6 OFFLINE   armorer_91F

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Posted Nov. 17 2009 - 08:20 PM

If anyone needs Army zeroing targets(the real deal) PM me with your addy.All I ask is that you pay me for shipping.


#7 OFFLINE   Quentin

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Posted Nov. 17 2009 - 08:46 PM

I have a Bushmaster XM15 E2S 16" flat top carbine with A3 removable carry handle(that's what the manual called it) and believe it or not the manual that came with it says to zeroing your sights basically like you said

And when I set my sights back to 6/3 and shoot at 25m the sights are dead on, unfortunately I've not had the chance to shoot any further than that yet.



Guess what, 'slowrider' - I believe your manual is wrong! And more importantly the US Army Rifle Marksmanship PDF says it's wrong. :laugh: That is if it says to zero at "z" for a carbine length barrel. You use that for the 20" barrel and zero at 6/3 with the carbine. Either will seem to work well close in but the truth of the pudding will be revealed at 300 meters.


#8 OFFLINE   armorer_91F

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Posted Nov. 17 2009 - 08:50 PM

Guess what, 'slowrider' - I believe your manual is wrong! And more importantly the US Army Rifle Marksmanship PDF says it's wrong. :laugh: That is if it says to zero at "z" for a carbine length barrel. You use that for the 20" barrel and zero at 6/3 with the carbine. Either will seem to work well close in but the truth of the pudding will be revealed at 300 meters.


We zero the M4 at 6/3 using the M4 zero target.I think it used to say go to the Z to zero but not anymore.I have a bunch of these targets and just zeroed my M4 this past weekend.


#9 OFFLINE   slowrider

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Posted Nov. 18 2009 - 12:55 PM

Guess what, 'slowrider' - I believe your manual is wrong! And more importantly the US Army Rifle Marksmanship PDF says it's wrong. :laugh: That is if it says to zero at "z" for a carbine length barrel. You use that for the 20" barrel and zero at 6/3 with the carbine. Either will seem to work well close in but the truth of the pudding will be revealed at 300 meters.

I don't doubt it a bit, my manual says

The A3 (removable carry handle) type rifles...

It don't specify 16" carbine or 20" full length. So I need to re sight my carbine at 6/3 instead of "z" right?

Thanks for pointing that out to me :)


#10 OFFLINE   Quentin

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Posted Nov. 18 2009 - 02:17 PM

I don't doubt it a bit, my manual says It don't specify 16" carbine or 20" full length. So I need to re sight my carbine at 6/3 instead of "z" right?

Thanks for pointing that out to me :)


Yes, for the M4 carbine set the elevation knob to 6/3 to do the standard 25/300 meter battlesight zero. Even better - first do the IBZ or RIBZ mod to your carry handle so you can click below 6/3 also to get the flatter trajectory. It's really not hard and you still can do your actual zeroing at 25 meters. You don't lose a thing but gain a lot. All you need is the 1/16" Allen wrench and possibly a new front sight post, about $10 with shipping. It was a piece of cake and you'll be proud of yourself!

The problem with your manual and the carry handle is the same ones get stuffed in the box with 20" rilfes too. In that case you would zero at "z" but not with the M4.

Edit:
BTW, Bushmaster uses the shorter A2 FSB instead of the F-marked one on their M4s and they realize that causes problems for some people. With a phone call they normally send you the taller sight for free.

Also, my M4 is a home brew from various parts. The carry handle I modded is a used Bushmaster, so this definitely works on Bushmaster.

Edited by Quentin, Nov. 18 2009 - 02:24 PM.



#11 OFFLINE   slowrider

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Posted Nov. 18 2009 - 04:46 PM

Yes, for the M4 carbine set the elevation knob to 6/3 to do the standard 25/300 meter battlesight zero. Even better - first do the IBZ or RIBZ mod to your carry handle so you can click below 6/3 also to get the flatter trajectory. It's really not hard and you still can do your actual zeroing at 25 meters. You don't lose a thing but gain a lot. All you need is the 1/16" Allen wrench and possibly a new front sight post, about $10 with shipping. It was a piece of cake and you'll be proud of yourself!

The problem with your manual and the carry handle is the same ones get stuffed in the box with 20" rilfes too. In that case you would zero at "z" but not with the M4.

Edit:
BTW, Bushmaster uses the shorter A2 FSB instead of the F-marked one on their M4s and they realize that causes problems for some people. With a phone call they normally send you the taller sight for free.

Also, my M4 is a home brew from various parts. The carry handle I modded is a used Bushmaster, so this definitely works on Bushmaster.

I don't doubt that a bit. thanks once again :thumb:


#12 OFFLINE   Quentin

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Posted Nov. 23 2009 - 01:25 PM

I was hoping this thread would get more comments. Guess it's pretty basic to old timers but a lot for a newbie to swallow. Anyway, if anyone sees anything wrong please let me know this noob would like to get it right... :laugh:

My main problem is I haven't been able to see if I'm zeroed at the longer ranges, over 100 yards, and probably won't till this spring. The holidays are in full swing and the weather is getting bad here.

Thanks!


#13 OFFLINE   WinSomeLoseNone

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Posted Jan. 04 2010 - 07:10 PM

Quick question on this.

This site http://www.ar15.com/...&...18&t=328143
informs you to set the bottom out point to -8 to give you easier movement to the -6 position because the sight base will not contact the carry handle.

If I set the elevation knob to bottom out at -8 as opposed to -6 does it change the POI distance from these.

25m: 6/3
50y: 6/3 -4 (for the 20" A4 rifle; the M4 carbine will zero at 41 meters/45 yards)
100y: 6/3 -6
150y: 6/3 -6
200m: 6/3 -4
300m: 6/3
400m: 4
500m: 5
600m: 6/3 (after one full rotation up


#14 OFFLINE   WitchingHour

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Posted Jan. 04 2010 - 08:02 PM

We zero the M4 at 6/3 using the M4 zero target.I think it used to say go to the Z to zero but not anymore.I have a bunch of these targets and just zeroed my M4 this past weekend.


I remember we did when we first replaced the M16s with the M4s (prior to this, the M4s were sporadic, and typically assigned to RTOs, assistant machine gunners, and medics, thanks to a CO who had the good sense to realise that a medic - authorised to defend themselves and their patient - can do so much more effectively with a rifle than just a pistol). It didn't take them particularly long to correct this, though, from what I can remember.
I'm wondering if the Santos method is possible with the Matech BUIS, and I'm also a bit curious as to how one would zero an M4 vs. M16 if they had a BUIS mounted which didn't have the windage adjustments (such as the Yankee Hill rear BUIS MarissaC uses on her rifle)


#15 OFFLINE   WinSomeLoseNone

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Posted Jan. 04 2010 - 08:08 PM

I remember we did when we first replaced the M16s with the M4s (prior to this, the M4s were sporadic, and typically assigned to RTOs, assistant machine gunners, and medics, thanks to a CO who had the good sense to realise that a medic - authorised to defend themselves and their patient - can do so much more effectively with a rifle than just a pistol). It didn't take them particularly long to correct this, though, from what I can remember.
I'm wondering if the Santos method is possible with the Matech BUIS, and I'm also a bit curious as to how one would zero an M4 vs. M16 if they had a BUIS mounted which didn't have the windage adjustments (such as the Yankee Hill rear BUIS MarissaC uses on her rifle)



You mean when they dont have an elevation knob. Most BUIS come with a windage and not an elevation adjustment. I know with the A.R.M.S. #40l BUIS you zero at 100 using the front sight post to make all elevation and the windage knob on the BUIS for windage obviously. I am assuming most BUIS are designed without an elevation knob intending to be zeroed at a specific range.


#16 OFFLINE   bonehead098

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Posted Jan. 04 2010 - 08:14 PM

My A.R.M.S. 40L adjusts windage only. {rear} My MI Front, elevation. {front}

Bone

My experience with these fine {DAMN} rifles/carbines is limited, but I don't recall seeing
any rear sights that wouldn't adjust windage.

Edited by bonehead098, Jan. 04 2010 - 08:20 PM.



#17 OFFLINE   WitchingHour

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Posted Jan. 04 2010 - 08:17 PM

Yeah.. elevation. Had myself a blonde moment there.
I was thinking the same thing regarding why they lack this, and question whether it's meant to be zeroed at 25 meters (military zero range), or if a company making these without a military contract for their product is going to do otherwise.
I should probably try that sometime.. zero in a rifle with the standard, carry handle-mounted rear sights, then see how the non-adjustable BUIS does comparatively.
Assuming I got my windage right with the rear BUIS after trying this method... let's say I'm shooting consistently higher or lower with the rear BUIS.. could the distance of the groups below the point of aim help to indicate what the appropriate range to zero in the BUIS would be (remember, this would be after doing a 25 meter battlesight zero with the handle mounted rear sights)?


#18 OFFLINE   WinSomeLoseNone

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Posted Jan. 04 2010 - 10:54 PM

Yeah.. elevation. Had myself a blonde moment there.
I was thinking the same thing regarding why they lack this, and question whether it's meant to be zeroed at 25 meters (military zero range), or if a company making these without a military contract for their product is going to do otherwise.
I should probably try that sometime.. zero in a rifle with the standard, carry handle-mounted rear sights, then see how the non-adjustable BUIS does comparatively.
Assuming I got my windage right with the rear BUIS after trying this method... let's say I'm shooting consistently higher or lower with the rear BUIS.. could the distance of the groups below the point of aim help to indicate what the appropriate range to zero in the BUIS would be (remember, this would be after doing a 25 meter battlesight zero with the handle mounted rear sights)?



I suppose it could. You could measure the elevation distance between the POI of the BUIS and the POI of the carry handle rear sight and calculate the drop in relation to the distance your firing and possibly figure out where the BUIS is designed to be zeroed at. Sounds like fun.

edit*
It would probably be easier to ask the manufacturer.

Edited by WinSomeLoseNone, Jan. 04 2010 - 10:56 PM.



#19 OFFLINE   MarissaC

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Posted Jan. 04 2010 - 11:03 PM

Don't encourage him. I'll the one who ends up stuck doing the math.


#20 OFFLINE   WinSomeLoseNone

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Posted Jan. 04 2010 - 11:18 PM

Don't encourage him. I'll the one who ends up stuck doing the math.


haha.

I am still trying to find the answer to my original question. If your so mathematically inclined maybe you can help.

Using the RIBZ and a 1/2 MOA removable carry handle if I adjust my elevation drum so I can set it back to 6/3 -8 so the sight base does not contact the carry handle and affect accuracy when shooting 100yds at 6/3 -6 will the markings on the drum still apply as standard like this.

Distance/Setting (y =yards/m=meters; up to 100 meters the difference doesn't greatly affect POI)
25m: 6/3
50y: 6/3 -4 (for the 20" A4 rifle; the M4 carbine will zero at 41 meters/45 yards)
100y: 6/3 -6
150y: 6/3 -6
200m: 6/3 -4
300m: 6/3
400m: 4
500m: 5
600m: 6/3 (after one full rotation upward)

I am worried that by making the elevation knob adjust to -8 as opposed to -6 it will change the settings for the ranges. ex) 6/3 will no longer be used for 600m or 300m...

Hope this makes sense.

Edited by WinSomeLoseNone, Jan. 04 2010 - 11:20 PM.






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