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Thread: AR-15 Zero Graphics - Various barrel lengths and zero ranges - M193, M855, and Mk262

  1. #71
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    Quote Originally Posted by Pappabear View Post
    Yes 50/200
    Absolutely, in my humble opinion.

  2. #72
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    Quote Originally Posted by Pappabear View Post
    Great thread. At the end of the day, doesn't the 25/200 zero offer the most consistent 25/200 hits without going full Metal jacket with barrel lengths and Ammo and guns and pixie dust. On average ?

    Best Minute of bad guy trajectories if your not trying to take an eyeball out with a Red Ryder. Or not?

    PB
    Yes and no.

    One of the most disappointing thing in every discussion about zeroes is that people seem to think that the user can do nothing but hold the dot/reticle/sight on the thing that they want to hit, and just have to accept that they won't hit once they get out past the second trajectory intersection.

    The next most disappointing thing is that people seem to think that a "zero" must place the point of aim in coincidence with the desired point of impact.

    I know that this thread is stupid long, and pretty much no one is going to actually read it anymore, but it's all just so dumbed-down that it makes me cringe every time I see it pop up in the list.

    There is a reason that just about every precision rifle is zeroed at 100 yards/meters, and not a single person using them worries about not being able to shoot past 150 yards. Why not? Because we simply manipulate the reticle to achieve the desired POI based off of highly reliable drop prediction. In precision rifle applications, virtually no-one is worrying about drop data being correct because we can quickly true that data and achieve consistent performance at least to the trans-sonic range, and with a little bit of work, well into the sub-sonic range. What are we most concerned about? Wind, and consistent windage hold references.

    So?

    If you have a reticle that is more advanced than a single dot or a front sight post, you can use that reticle for the exact distance (or distance envelope) that you need, regardless of "zeroing scheme" used. A 100 yard zero distance will provide the user with a higher confidence in establishment of the actual ballistic baseline than anything closer. A POA/POI intersection at 100 yards provides the most consistent hold, with the largest error budget on a 3-5" target, from 5-150 meters (164 yards), where most fights happen, even with contemporary tall optic heights (3.2" LOS over bore) and 77gr SMK from a 14.5" barrel at 2500 f/s. With that trajectory slope, the impact will be 2.9" below the zero reference at 5 yards, and about 0.9" at 50 yards; a 2" difference. With a 50 or 200 zero, that is instead a 2.9" difference, which eats into the error budget for a precision shot, and thus the consistency of the hold-over for precision shots where the exact distance is not known. Using a 100 yard POA/POI zero or trajectory allows the user to tightly constrain the POI by simply applying a 1.5" (ish) high hold above the desired POI. At 5-10 yards that places those shots 1.4"-1.1" below the very center of the target (2.9-2.6" below POA), pretty much perfectly centered on the target at 30 yards, and about 0.7" above the very center of your target (0.8" below POA) at 50 yards. This employment window accepts that your group sizes will be smaller at closer ranges, so sitting toward the bottom of the 3" target isn't hard to keep inside the target circle, puts the shots toward the target center at the most critical area of use (20-50 yards), giving you the most error budget where likely to have to really fight it out with small, moving, short exposure targets, without having to process distance estimate at all. Just hold about 1.5" high and let it fly.

    Past 50 and out to 150 or so, just go straight in. If you can live with a 2" low shot, that distance reaches 175 yards, but average group size at 175 yards in the field is going to be around 5", so that may not be the best choice for a target that is constrained vertically. The gentle slope on both the approach to and departure from the 100 yard zero point makes these windows very tolerant to ranging error as is very common at those distances.

    At 200ish yards (175-225) hold high in the target area, as the drop is going to be between 2" and 6", with an expected precision level of 6" or so. If you have a reticle with a drop reference, this is were you're going to start using it. At 200 my hold is 0.5 MRAD, with a pretty generous error budget: 0.2 at 155, 0.8 at 235. There isn't much out there with a size restriction that would make me nervous about a 0.3 MRAD vertical error at 200 yards that I'm going to use a 5.56 carbine on without more firmly establishing distance.

    At 300 you're starting to get into the "you need to be fairly precise with your range" area. A 1.5 MRAD is going to be called for 300, but a 50 yard error is going to hurt you on anything smaller than barn-doors, no matter how you zero, and you're simply not going to have the time to do that if you're in a hurry.
    I laid out a nearly "worst case" scenario for 5.56 in relation to a 100 yard zeroing approach above. A faster projectile launch flattens that out even more.

    Let's take a step back and see what this looks like with a 200 yard zero (200, not 50, because zeroing at 50 is pretty much admitting that you're not going to shoot past 50 yards or else you would be zeroing at those distances):
    If you try a 1.5" high hold, you wind up being 0.8" below the POA at 35 yards rather than 50 yards, initiating a precision hold changeover much sooner, and with less overlap. So then you wind up going straight-in at 35-70 yards (0.8" below to 1" over POA), and then you need to start working hold-unders from 70-135 or so for precision shots (which really isn't bad with irons, but doesn't really help anything else). You still run out of steam before much past 250, requiring a new POA or reticle reference anyway.
    So, you shot at 50 yards (getting a much lower-confidence zero than just about anywhere further), have to do more mental math in the most lethal areas of a gunfight that we're theoretically getting the rifle set up for, and gain a whopping 30 yards of additional range based on POA/POI expectation at a distance where maybe 5 people in the US have engaged in actual gunfights, that would be better addressed by using a targeting reference in the aiming device that allowed you to choose specific range POI.

    But I'm using a red-dot...
    It's going to be challenging to even see the thing you want to shoot at 200 yards if it isn't in stark contrast with the background, and good luck with spotting impacts.

    And this is all without even getting into wind.

    A LPVO with a decent reticle for drop holds and wind reference, zeroed at 100, will let you do more than cling to a specific POA/POI intersection distance. If you want, once you zero at 100, you can pop on whatever adjustment you need for the distance at which you are most likely to be shooting the most important targets. A 200 zero won't do me any favors if everything I need to shoot is 300 yards or more away, but I can apply a simple mid-range hold or adjustment to put me right where I want to be with more leeway.

    While I do use a 100 yard zero baseline for a lot of stuff, that doesn't mean that I'm stuck there. Even if a gun has a 200 yard zero (due to BDC or whatever), I retain the right to use other parts of the reticle or apply an adjustment for the condition that I am in when I need to use the rifle. I definitely use a 200 zero for stuff at 200, but what really matters is that I can instantly apply a 742 yard zero based on my ballistic data and my 100 yard baseline, and then immediately change to a 326 yard zero by either holding or dialing.

    We aren't tied to or beholden to that zero distance, and nor do we have to have POA/POI intersection at that distance. Zeroing at 100 yards irons out a lot of errors and stabilizes some unknown variables. We obsess over one or two clicks when shooting at the range, but gather no experience in real-world wind estimation or compensation at those distances at which we fear so much that we seek to baseline our rifles there, but without bother to actually do it. We'll get mad about an argument on the internet about someone else's purchase or opinion, but we don't bother to learn how to use reticle relationship to determine target distance to within a couple dozen yards. We'll tell people what kind of adjustments they need in their optic, without knowing what an average target size is in those insisted-upon angular amounts. There is much to be gained in individual performance by simply shooting groups at 100 yards in varying positions and time constraints, and it serves as a nearly inarguably useful reference.

    So is a 50, 200, 100, or 538 yard (meter?) zero the best? Nope. Ain't no "best" if you don't know what to do with it and don't shoot the actual distance that you are trying to be successful at. And life doesn't happen in neat little hundred-yard increments.

    Whatever you think you want to do, go prove it. Want to do a 2.5" low at 10 yards zero? Awesome! Go do it and see what it does at distance. Want to do a 500 yard POA/POI zero? Great! See how it does at 10, 25, and 50 yards. Think you have everything wired tight? Super! Go shoot some matches that have practical targets at irregular distances and see where the wheels come off. When it all comes down to is that *really* the distance at which you are shooting is irrelevant if you have sufficient data to be able to accurately predict where the projectile should be hitting at any given distance; all the shooter must do is establish the correct reticle/adjustment relationship at the distance available and work backward to achieve a proper "other distance" sight setting.
    Jack Leuba
    Director of Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  3. #73
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    Quote Originally Posted by Failure2Stop View Post
    --- long post above ---
    Thank you Jack. This is a goldmine of information! Very informative and interesting.

  4. #74
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    Great post.. Thank you

  5. #75
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    The great thing about the 36yd/300yd zero is you can aim center of mass from 0-350 yards and hit the target without any need to hold over. If those charts posted by Vandal 5 included 350-yard POI you would see it near the bottom of the main box (opposite the 200-yd POI). IMO this is the most versatile zero for red dot scopes without a BDC reticle. You don't have to think about anything. Look where the 300-yard POI is on the 50 and 100 yard zeros, all are outside of the box.

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