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Posted: 4/19/2005 4:43:21 AM EDT
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My EO Tech just came in yesterday (thanks SWFA), BUIS from Bushmaster scheduled to arrive tomorrow. All for a new rifle. Now that I have all of these sights, is there a protocol for zeroing? I'm assuming I should zero the irons first, then mount the 511 and zero that. Is this correct? Is there any point to zeroing the original sights on the carrying handle? Thanks. |
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Most folks use the IBZ 50 yard zero from here: groups.msn.com/TheMarylandAR15ShootersSite/zeroingmethods.msnw FWIW, yes I'd zero the carry handle (just incase ya need it later) As to EO or irons first, don't think it matters.....  Mike |
But can't you zero the EOTech with the reticle anywhere in the screen, and then just place it on top of the post when you shoot? WIZZO |
I’m not sure........I guess you could do it that way. Just seemed easier to zero the irons, then simply adjust the EOTech to the top of the front sight post. Kind of gets you in the ball park, minor adjustments might still be necessary. Saves ammo also. I could be wrong but I look at it this way. It might take you, for example, 10-15 rounds to zero and confirm your irons. If you then zero the EOTech separate it may take another 10+ rounds. If you adjust the EOTech to sit on the front sight post after zeroing irons you might only need a couple rounds to verify the EOTechs zero. YMMV, but this method made sense to me and it worked. |
I'll second the IBZ; I think it's the finest zeroing method out there. |
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Okay I was wondering what type of target do you use to zero at 50 yards, I was trying to use some military 25 meter zero target's blown up a in size to 11"x11" and at 50 yards it was hard for me to really see the target. I would really like to know if thier is another type of target I should be useing to zero my BUIS and my optic's at 50 yards. 
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There are targets made for zeroing, you can find some printable ones on the website mentioned above with the IBZ method. THese targets have grids for easier adjustment. I just use any target that works well for me. I can estimate the distances well enough I don't need the grids. I found a standard small bore 100 yard target worked fine. The big black circle was pretty close in size at 50 to the reticle of the Eotech |
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For a 14.5" barrel AR with standard military ball ammo, the aiming error puts the best distances for zero at 38 yards and 252 yards. This will provide you with the least error for movement between 0 and 300 yards. Since most ranges don't have a 38 yard area, you can counter the effect of the distance by shooting at 25 yards/meters. Use your standard military A4 target, and aim 2 grid squares(1cm between dime size impact areas) below center mass while keeping your point of impact at the true center mass. All of this info is for the EOTech sight and takes into account the distance of the reticle center above boreline from the rail of the upper receiver. If you aren't going to be moving between distances and only shoot at 50 yards. Then zero at 50. If you want a customized 25m A4 target designed for the EOTech sight, email me and I'll send you a copy in PDF format. |
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I have an EOTech and I recently switched to a 14.5" M4 barrel. I am just wondering why the way you mentioned is better than the 50 yard zero? I am going to be sighting in both my EOTech and back up iron sights this weekend, so any information is appreciated. FWIW, my BUIS consist of the normal front sight base and an ARMS 40L. |
This makes zero sense IMHO. Asumptions - 62gr round moving at 2900fps at 78', std conditions at 1400' ASL You have to zero at a non standard range (38y), and as it's a shorter range you induce a little more error. Then you have a ballistic trajectory of + 3.8" at 175y almost 3" high at 100y) With the 50y zero you zero at a common range distance - and you have a trajectory of +/- 2" from the muzzle to the about 250yards. Being only 6" low at 300y. So the 50yard zero has half the error of the 38y zero to well past any likely shooting distances with a carbine. |
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Here is the sense: The bullet arc has the largest error at 150 yards and 300 yds. The least amount of error is seen at 38 and 252 yards (the arc rising and falling at the static line on a ballistic chart). Any ballistic software will calculate this. You have to take into account the grain weight, muzzle speed velocity, but also the ballistic coefficient, its shape, etc. Any way, those calculations are done specifically to military ball M855 (SS109, C77). You don't have to zero at a non-standard range. On a 25m military zero target you put the point of aim two grid squares south of center mass, and keep your point of impact in center mass. It accounts for the change in distance relative to the point you're standing at (in this case 25m range). The lowest percentage of aiming error for an EOTech holosight (this takes into account the distance the reticle center is above boreline, assuming it is mounted directly to the upper reciever) between the distances of 0 to 300 yards is a zero at 38 yds. If you are only moving in between 50 and 250, then zero at 50 (better yet, calculate the least aiming error for that distance range and zero at it). If your running lanes that cross the 0 to 300yds range, I encourage the 38 yd zero. There's the 101st, 82nd, Stryker BDE, and USSOCOM that have the modified target for EOTechs in place to the units who are aware they exist. They're the subject matter experts who're employing it. |
Really no kidding? I've never heard of this! As I plainly posted I used M855 from an M4 with an EOTech mounted on a flattop (2.6" HOB). Your 38 y zero has a 3moa error at 100y and still a greater than 2moa error at 175y. By contrast the 50y zero has a 1.6moa error at 100 and it's greatest error is at 300y (2 moa). So for distanaces of likely engagement (80% is 200y and under) the 50y zero is more precise. The only time the 38y zero is more accurate is at 300y - where so few engagments take places it's not worth mentioning.
Yep adding in more error when zeroing.
"Percentage of aiming error" - what kind of lawyer doublespeak is that? You want the smallest variance from the point of aim - which the 50y zero accomplishes. What are you using for the HOB? There's the 101st, 82nd, Stryker BDE, and USSOCOM that have the modified target for EOTechs in place to the units who are aware they exist. They're the subject matter experts who're employing it. Remember these 'Subject Matter Experts' gave us the 3+1 zeroing procude which has been shown to be WAY off. I'd also point out other 'Experts' (guys who've used the weapons in the field) pretty much all teach the 50y/200M zero. |
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For those playing at home... This is a plot of the trajectories:  As you can plainly see the 50y zero procedure produces a flatter trajectory, is more consistant, and is more precise till out past 250y. Past that the 50y zero is less only around 1 moa in error, below 50y the difference in the trajecotories is less than 0.5". Trajectoreis were made assuming M855 from an M4 using a flattop mounted EOTech HOB 2.6" M855: .308 BC moving at 2970 fps @ 78' Env: 1400' ASL std conditions Drag: G1 By the numbers:
Edited to try to get the table to display correctly |
Correct - as that is what Mr. DFinegan referenced in his postings. However there is very little difference between the 14.5 & the 16" when you graph them, Even changing the rounds (say to M193 or Mk262) effects the results minimally IMHO. |
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Forest, First off hand let me say I appreciate the sarcasm (seriously). I'll explain my "lawyer double speak" also, but in the interim, you'll be comforted in knowing all three of the words percentage, aiming, and error appear in every English language dictionary available. I'm sure thats a load off your mind. I'd say that it'd be more like mathmetician double speak as the only law involved is that of gravity, but thats physics. Ah, who cares. Point is, you're correct to an extent. If my only engagements are between 50 and 200 yards, then you SHOULD zero at 50. Which is what I mentioned above. If your needed range with the least amount of error is not 0 to 300 yards, then zero your rifle at the better distance (i.e. 50 yds). A couple of things I'm interested in to hear from you. What is the formula that you use to determine the deviation from point of aim. Your numbers appear to be slightly off. The max point in the arc for a 38 yard zero is 3.4 inches (rounded/approximate) and 1.6 for a 50 yd zero (rounded/approxiamte). No big deal in terms of getting the same point across; the arcs look the same. I'd also like to know where your info comes from pertaining to most engagements being under 200 yds (I'm not discounting it, it makes sense; its surprising Trijicon does so well, then). Now, the percentage of aiming error refers to, I'll try to be clear, the overall lowest percent amount of deviation from the point of aim throughout the range of 0 to 300yds. For example, if you add up the percents (or the actual numbers to get the mean deviation) of deviation from point of aim over the course of 0 to 300 yds for every possible zeroing distance throughout that range, the lowest percent across that range will be from 38 yds. If you were to do that from 0 to 200 (you're majority of engagements) you'll get a different lowest percent (in your opinion 50yds). I haven't done the math yet on the latter, or I'd tell you the best distance (and you may be right at 50). Also, you see a very distinct drop at about the 220 yd mark with a 50 yd zero, and it plummets significantly from there. I guess you can always wait for the target to get closer...but then you'd be a better target as well. I typed the backwards version of the adjustment on the target. You aim center mass, but your point of impact will be about 2 grid squares lower (assuming a dime sized group) exact measurement is a little more than 1cm down. Please explain the adding in more error by lowering the point of impact on a 25m target. It accounts for the fact your target is not sitting at 38 yards. Simple math. Also, if you're interested in exchanging data, please email me. I'm new to site, and am not clear on posting the graphs and formula data I have. I'd be happy to get your input. You seem pretty knowledgable on the subject. Have fun. |
And none of which makes any sense to a soldier who's shooting at the enemy. He want to keep the round as close to sight line as possible for as long as possible in order to minimize errors.
Please look at the data carefully. With a 50y zero the round his the LOS at 200M (roughly 218y) at a little beyond 250y the round from the 50y is just as far BELOW the LOS as the round from the 38y zero is ABOVE the LOS (roughly 2"). So the 38y zero really doesn't have an accuracy advantage till you get past 250y.
I uses 3 different pieces of software, as doing the numbers by hand takes so much longer.. 1) PBX its a ballistic calculator that runs on Palm OS PDAs. Great because I can take it with me to the range. 2) I have a spreadsheet (Excel) that also runs the forumals 3) When I don't have access to the above (or I need some data points they dont cover) I use the JBM online ballistics calculator. All 3 of these produce results within 0.1" under most condidtions. I can understand some variation of a few tenths of an inch if you vary data like Height over Bore (2.6" is standard) or environmental conditions. Also all my calulations use a MV taken at a specific distance (with M855 it's 78' per the military spec - with M193 I use 15' per the military spec). If you use the published MV but put in a measured distance of 0 then you'll also get slightly different numbers. FYI you can download #1 & #2 for free from www.MD-AR15.com in the Documents area. I've got a link to the JBM Ballistics calculator posted on the main Zeroing Methods page on that same site. I would be interested in knowing if you're using s/w or calculating out by hand - and what specifics you are using for the variables (HOB, MV, Chrono Distance, Alt, Atmos Conditions, BC, etc.)
"Operational Requirements for an Infantry Hand Weapon" by Norman Hitchman (aka Hitchman Report). Call number UD 390.H5 1952. FYI From the AARs I've heard about in Iraq it seems to be keeping with the Hitchman report.
The problem is those are the kind of 'numbers' that Lawyers and Mathmeticians use. and are not meaningful in the real world of small arms. For example, look at the chart. Till around 43 yards or so the 38 zero is closer to the LOS. But it's never more than 0.5" closer. Statistically the 38y zero is almost 2moa more accurate at 25y than the 50y zero - but that value is meaningless as that translate to 0.4" (2 bore diameters). Is 0.4" at 25y going to make a difference in a fire-fight? Not in the least. Now lets look at the 100y variances. At 150y the 50y zero is 2" high, while the 38y zero is showing rouhgly 4" high. is that important? Maybe yes maybe no. If an enemy sticks his head out from behind cover it might be the difference between a hit and a near miss. However, if the Soldier is going for a COM shot as the enemy makes a rush - it will make no difference as the target is so big. Now well move out to 300y - where the 38y is shines. If an enemy sticks his head up the 38zero will do the job while the 50y zero's round will strike the cover, but will the Solider even seen an enemy's head at 300y? That is a small target (3 moa) and in the unlikely event the soldier does see it, odds are he won't make the shot (see above study). Now if that same enemy is walking at 300y and our soldier decides to take a shot it will be center-of-mass. The 38y zero will nail the enemy at point of aim - the 50y zero's round will be 5" lower (2.5moa) - the results in either case will be the same.
A 5" drop at 300y is essentially meaning less (as pointed out above). Micro Terrain will be more important than the range.
If you are using a grid point and it's EXACTLY were you need it to be then there is no additional error - however I am suspect that the grid point would be EXACTLY where you need it to be. When we zero at close ranges (25M, 38y, 50y) it's for the first crossover of the trajectory. However we usually refer to zero's as 200M zero or 300M zero. You know as well as I small errors up close translate into much bigger errors when they are expanded outward. For example a shift of 1/4" at 25M translates to a 3" shift at 300M. With a 50Y zero any error is 'only' magnified by 4x at 200M (or 6x for 300M); however zeroing at 25M results in errors getting magnified 8x at 200M and 12x at 300M. Is this an academic issue or is it really important? That's a personal choice. But as the Army only requires it's soldiers shooting to 6moa capability, I'd rather reduce the chances of error as much as possible (fine tuning at the far crossover point is optimal).
I'll send you an IM with my personal e-mail (or you can use the above button). I'd like to keep most of these discussion on there though so every one can learn, and there are others on this site knowledgable on the subject who could put in their $0.02 I'm also going to take this time to note EITHER zero will work. Most of what we're discussing is academic minutia. There are a few (very few) instances when the IBSZ (50Y) will have a meaningful combat advantage over the 38y zero. However few civilians/LEOs have access to a 25M range (27.3y), but 50y ranges are very common. |
Man both of you just confussed the fuck out of me.  I guess i will go camp out at the ramnge and shoot the shit out of my target's until I get zeroed.DFinnegan thanks I got the target's you emailed me and i will print them out and blow them up in size so I can use them at the range. 
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