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Discussion Starter · #1 ·
im sorry in advance if this has already been done to death but ive done a quick search and its not producing quite what im looking for. its been a while since ive had to qualify with the m16a2 and my memory is beginning to slip.

im going to zero my m4 but the elevation settings are a bit different than its long barrel counterpart and it gives me a mountain of questions.

1. is the zeroing distance going to be different? (the m16a2 was zeroed 36 yds and the round would re-intersect the line of sight at 300 yds if i remember correctly)

2. i assume the "z" on the knob is for zeroize(2 clicks above 6/3), is this where its supposed to be while zeroing?

3. after adjusting the front sight post, if this "z" setting puts the group in the bull at 300yds(in theory), what yardage would be a hit in the bull at 6/3?

4. my elevation knob only goes to 1 click below 6/3, is this as it should be or does in need adjustment?

im sorry again if this has all been repeated over and over. i guess i could just go out and shoot and get some answers for myself but my fundamentals arent what they used to be so i cant tell if my groupings are consistent hits or consistent flaws. all help is appreciated.

6 Posts
Discussion Starter · #3 ·
nevermind! i found it! but for those of you who are currious as well...

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.armystudyguide.com/content/army...6a2-rifle.shtml Battlesight Zeroing the M16A2 rifle (for the M4, remember to zero at 6/3)
http://ohmr.ohio.gov/forms/ohmr2444-b.pdf Download Free M4 25/300 meter zeroing targets
http://www.bobdbob.com/~deneb/doc/targets/m16a2-25m-zero.pdf Download Free M16 25/300 meter targets
http://www.usaac.army.mil/amu/ServiceRifle/M16-M4%20data.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.bushmaster.com/products.asp?cat=21

Once the M4 is zeroed in you can click below 6/3 four clicks to have the IBZ ranging scheme that’s within an outstanding 2.5" of line of sight from 0 to 230 meters! That’s 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/guns/ImprovedBattlesightZero.pdf the Improved Battlesight Zero
http://www.m4carbine.net/showthread.php?t=22 more about the Improved Battlesight Zero
http://www.ar15.com/forums/topic.html?b=3&...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.)

706 Posts
Really just depends on the intended use, ammo, and velocity.

There will be a sweet spot.

Let us know what ammo you will use the most and we can get you close.
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