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"Long range" shooting, scope levels, ballistic calculators and such.

Discussion in 'Rifle Country' started by MCMXI, Oct 18, 2020.

  1. MCMXI
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    MCMXI Contributing Member

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    The point of this thread is to remind myself and others that the devil can be in the details. It can be very frustrating when you can't hit a target at "long range" particularly if you don't know why. There are so many variables and when things don't go right we can start questioning everything and that can erode confidence in the equipment and oneself. My apologies if my thoughts in this thread aren't organized but it's late ... so here we go!

    I bought a Tikka T3 TAC NS back in July from a friend and have been impressed from the get go.

    https://www.thehighroad.org/index.php?threads/new-used-rifle-tikka-tac-ns-300-win-mag.871202/

    I'm planning on using it for deer and elk this fall and have had very good results shooting 180gr Federal Premium Vital-Shok Trophy Copper (.300 Win Mag). This afternoon I wanted to check the Applied Ballistics dope out to 700 yards and the app on my phone was spot on with corrections of 0.3 milrad at 200 yards, and 1.6 milrad at 400 yards. The app called for 4.0 milrad at 700 yards (assuming a 0 degree angle to the target) with 0.1 milrad of spin drift to the right. That particular target is probably 10 to 15 degrees up angle so I figured on 3.8 mils of correction for elevation. So here we go ... holding off the left edge of the plate but centered for elevation ... MISS .... MISS .... MISS! I couldn't see where I was missing with the first three shots but on the fourth shot I saw splash just to the outside of the bottom right corner of the plate. Once I knew where I was missing I was able to dial up another 0.3 milrad, hold off a little more for wind and then DING, DING, DING ... I could hit the plate at will but hits were to the right of center, at least a 1/4 plate right and more like 1/3. Hmmm ... it didn't seem that windy.

    I have a few of the HORUS ASLI units on some scopes including the NF on this Tikka. I thought I'd leveled everything up a few months ago, but when I leveled the top of the 100 yard target backer board and aligned the reticle to the board I noticed that the HORUS bubble was way off. When I install a scope I use feeler gauges to get it level to the receiver/rail, then use a bubble level to get the HORUS level with the reticle. I'm not going to do that anymore, not the last part anyway. This afternoon I assumed that the scope was true to the rail (based on feeler gauges), aligned the scope reticle to the 100 yard board and then readjusted the HORUS so that the bubble was in the correct position.

    So now back to the 700 yard plate. The next 5 or so shots all landed in the center of the 12" plate holding 0.5 milrad off the left edge (8 to 10 mph wind) but centered for elevation. Finally I went back into the Applied Ballistics app and edited the ammunition data by guessing G1 BCs for different velocity ranges until the data appeared to match my results out to 700 yards at least. The problem with G1 BCs is that they don't account for velocity. I have a high level of confidence in the MV that I measured using a LabRadar system so the only option is to adjust the BC over a few velocity ranges. I need to do that for other G1 based ammunition profiles that I set up in AB.

    If someone would check my math and let me know if I'm thinking about this correctly. If I'm dialing up 4.2 milrad for the 700 yard target, and have a 5 degree clockwise error in terms of reticle/scope rotation from level, I'm inadvertently dialing in 0.37 milrad to the right which at 700 yards is 9.2" to the right. Even at 2.5 degrees of error, I'm dialing in 4.6" of horizontal error. Does this make sense?

    There are many variables to control in order to make first round hits on small targets at longer ranges, but having a level scope is one of the variables that we shouldn't have to worry about. In the bottom photo, it takes a tiny rotation to get the bubble to peg to one side or the other so as long as the bubble is off either extreme I feel that the scope is more than level enough.

    nf_reticle.jpg

    horus_level.jpg
     
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  2. Ru4real

    Ru4real Member

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    Your logic makes sense to me, so either we are both on to something or we are both nuts.

    I also check horizontal cross hair against something I’ve measured level at distance once the rifle/scope is plumb and level.

    A simple test to confirm the bubble / plumb checks I like to do is in one sitting, shoot paper in 100y increments from 100y to 600y, 3 rounds at each distance. Then look for diagonal errors that get progressively worse with distance in each of your 6 targets. This is a good final check to confirm a level, plumb, square scope, among other things. Shooting all 6 targets in one sitting on a calm day is the important part. And then test again later on a windy day to confirm your scopes’ windage marks.

    I only use ballistic charts to get ideas. I practice shooting to get the feeling and intuition.
     
    Last edited: Oct 18, 2020
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  3. MCMXI
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    MCMXI Contributing Member

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    @Ru4real, there have been a number of discussions on this forum about cant error but this is the first time I've actually bothered to calculate it. If someone sees a flaw in my logic please let me know, but the schematic below shows that a small cant error can be significant in terms of windage error. Having a bubble level on a rifle or scope that actually correlates well to the reticle isn't a bad thing. If the target isn't level and there are no reference points, it's quite easy to be off by 5 degrees or more. Rifles tend not to fit us that well and most will cant the rifle to get the butt situated in the shoulder naturally and comfortably. I have a little challenge set up for myself to make first round, center of plate hits on steel at 100, 200, 400 and 700 yards regardless of the conditions. Correcting the HORUS on the Tikka should increase my chances with that rifle/optic combination, and if I miss it's most likely due to a bad wind call.

    E.g. If you dial up 4.2 milrad for a 700 yard target with a 5 degree canted reticle, the windage error can be calculated as follows:

    X1=Y1 sinΦ
    Windage error = 4.200 milrad * sin(5°)
    Windage error = 0.367 milrad
    At 700 yards, 0.367 milrad = 9.22"

    cant_error.jpg
     
    Last edited: Oct 18, 2020
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  4. Walkalong

    Walkalong Moderator Staff Member

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    Always start with the rifle level. Use a quality level that shows the same thing either way you put it. Some don't jive when you switch them around.

    20191206_154807.jpg 20190618_183256.jpg

    I used a plumb bob and black cord to set the reticle on my two PRS two rifles, as well as my .308. Since I have had no trouble hitting targets at distance when I have the velocity right, I am assuming they are mounted correctly.

    Velocity is key, which is why long distance shooters want small ES/SD numbers, and why they check zero and velocity often. Barrels change as they wear.
     
  5. Ru4real

    Ru4real Member

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    Agree.
     
  6. taliv

    taliv Moderator Staff Member

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    Agree with walkalong. I hang a long plumb line and have a level on my gun. It’s not a particularly high quality level but it’s the one that stays with the gun when I’m shooting so it’s the important one. And then I rotate the scope until it’s aligned with the plumb

    I stopped doing the feeler gauge method a long time ago
     
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  7. MCMXI
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    MCMXI Contributing Member

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    Interestingly, a 5 degree cant error makes a much bigger difference at 700 yards than +/- 25 fps. Are the targets at PRS matches typically level?

    @taliv, where are you placing the level on your rifle when the scope is mounted? I've used levels on rifles in the past but it's not always easy to find a suitable spot. A former boss bought me a really nice Starrett level about 10 years ago that I've used on some rifles. I think I'll continue to use a leveled board at 100 yards to achieve the same thing that you and @Walkalong achieve with a plumb bob.

    starrett_level.jpg
     
    Last edited: Oct 19, 2020
  8. Walkalong

    Walkalong Moderator Staff Member

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    You can substitute a level board for the plumb bob, but the rifle still needs to be as level as you can get it.

    Yea, cant will get you, but assuming the scope is mounted correctly, having the wrong velocity in the ballistics program is the biggest reason I have seen/experienced for vertical misses.

    PRS targets are just steel hanging up, so they should be close to level, but of course some of them are round, and we are abusing them, all depends on how they’re hung and what shape the plate/hanger are in.

    That’s a very nice level.
     
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  9. taliv

    taliv Moderator Staff Member

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    1911,
    i have bubble levels built into the spuhr mounts, but being left handed, i can't see it easily without disturbing my position. so i put one of these in front of it https://www.amazon.com/Metal-Spirit-Bubble-Picatinny-Weaver/dp/B07JKQVR8Q
    618RBRpPw9L._AC_UL160_.jpg

    you can spend hundreds on bubble levels, or "anti cant devices" if you please, but i've had a bunch of these $8 ones and never had a problem lol. i like that it is low, so i'm not having to look so far up to see it. and i like that it sticks out a bit, clear of the ocular housing so i can switch my focus to my eye that's not looking through the scope, and see it without breaking position. it also doesn't stick out as far as other things, like bolt or scope knobs etc, so it doesn't hang up or get bumped

    i jam it right up against the rings
     
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  10. Varminterror

    Varminterror Member

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    The answer is “typically no,” but we adapt to the terrain features or obstacles.

    Most PRS shooters (I hesitate to say all, but it’s probably very close to say all rather than most) have bipods with the ability to cant/swivel to correct rifle tilt, and independently adjustable legs to correct tilt if necessary, beyond the capacity of their bipod’s cant/swivel head (note - using “swivel” synonymous with cant here, not with pan. Harris uses swivel to describe their tiltable design, Atlas calls it cant). Secondly, typically around half of each PRS match is “positional shooting,” fired with the rifle sitting on a bag supported by an obstacle, and the shooter remains to have control of how the bag and rifle are positioned to keep the rifle level.

    I don’t use the same model, but I use a similar layout as @taliv, carrying my level out to the side. I use Vortex bubble levels on my scope tubes, positioned on my left side (right hand shooter), just forward of my parallax knob (or windage on Kahles) so it is visible while I’m in the scope. This puts my data card and level arranged in sort of a “heads up display.” I think I pay $30 for the Vortex levels...? Cheapest bit of kit I have on the rifle - no excuse to not have it.

    4A29343F-B19D-4DC6-AA95-B1C0C41703A7.jpeg

    I install my level onto the scope on a jig. I level the jig to the world, use a level on the adjustment knob to start, then confirm against a trued tall target (or plumb bob line). With the scope locked onto the heavy jig, I dial up and down to confirm it tracks along the line as well (confirming the reticle is actually collinear to the elevation adjustment). I check again on the tall target once the scope is mounted to the rifle - level on the rail begets a level clamped to the barrel to ensure the rifle is level. And of course, then it’s all fired at range on a tall target to be sure it stays on line as dialed and held. I’ll dial up and down shooting at the tall target, even dialing too much for my target size and holding back under in the reticle to get a taller span to fit onto the target.

    5177A185-14DB-43D1-A1B2-4094B412D56D.jpeg

    More to the original question asked, the trigonometry is pretty simple. I made this infographic 6 yrs ago for a similar discussion - it was a hunting forum so I used a 30-06 at 300 yards as the example, examining an extreme 10 degree offset, but the math applies to anything. This compares a level rifle with the scope reticle in line with the bore to a rifle with the reticle NOT aligned, and then held with the rifle level or with the reticle level. Extend this to 700-800 yards, and those offset errors become that much more significant. Shrink the deflection error down to a more realistic equipment and in-field error (far, far less than 10degrees), and the offset error becomes less and less significant. Hence leveling the reticle and using a level on the rifle/scope is cheap insurance. This depicts a hold over for illustration purposes, rather than dialing, but the result is the same (assuming the reticle is aligned as designed with the elevation adjustment). The orange dots represent the targets in the sight pictures, whereas the green dots with Xs on the targets below represent the corresponding POIs.

    32CFEAC3-37FE-45F3-A78A-734FABD19B47.jpeg
     
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  11. MCMXI
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    MCMXI Contributing Member

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    I bought a few of those HORUS ASLI units quite a few years ago, three I think. I've bought all manner of bubble levels over the years including some that were branded US Optics, but as you point out, an $8 bubble level can do the trick just as well. The important thing is to have a level that's trued to the rifle and optic, and use it.

    @Varminterror, thanks for the excellent post. I want to make the point again that the intention of this thread is just to get folks thinking about cant error when shooting at longer distances because it can cause a lot of frustration. It doesn't matter what bubble level system you buy, or how you true everything up, the important thing is to know that it's a real issue, and that it can be corrected for. @taliv has made the point that it can be corrected for as little as $8.
     
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  12. MCMXI
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    MCMXI Contributing Member

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    @taliv, I have three Spuhr mounts on my AIs with integral bubble levels, but to be honest they're a bit close to my face so hard to see (for me at least). I might need to add a bubble level or two as you do.
     
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  13. Varminterror

    Varminterror Member

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    @MCMXI - I agree, it’s important enough to spend the (small sum of) money to reduce or eliminate your risk of cant error. I don’t put bubbles on every rifle, but I do on anything and everything I want to dial or hold for range.

    That 1/2” error, or even the 2”x.2” error I depicted above might not seem like much, but that’s only 300... missing by 5” at 800 because of a canted rifle doesn’t seem responsible.
     
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  14. Walkalong

    Walkalong Moderator Staff Member

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    Why demonstrate holding 4 MOA under instead of over, or am I looking at it wrong? Curious.

    If you have a canted reticle, but the rifle is level, the center of the crosshairs is still centered over the bore, so hunters who don't need to hold over/under will never know the difference.

    When you get in trouble is when you use a spot other than the center on a canted reticle to aim at your target/intended POI.

    Of course if the reticle is canted, and you roll the rifle to make the reticle straight up and down, you're crap out of luck, like example three.
     
  15. Varminterror

    Varminterror Member

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    @Walkalong - I didn’t do a great job describing the graphic, trying to be more succinct than I was in the original forum post for which it was created, but it does reflect 4moa hold above target. Assuming an 8moa wide duplex (should probably remake this using a Mil-hash reticle and a 6.5 creed at 800 instead of a duplex reticle with a 30-06 at 300) - the tip of the bottom wide bar is 4moa hold over, so placing the bottom bar on the target (orange dot), we’re holding over 4moa.
     
  16. d2wing

    d2wing Member

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    The key is that the center of the bore is directly under the center of the scope, and that the cross hairs are level so both are on the same vertical plane You can use levels to achieve this and I do that and to check I sight against a building edge or something I know is plumb. A plumb bob works great too. If the plumb line intersects the center of the bore and scope you should be good and at the same time you can check the horizontal crosshair bar against a roof line etc. I also bore sight this way. And hope the carpenter was a good one lol.
    When shooting I try to observe a known vertical or horizonal to avoid canting. A scope level is great but I don't know how to look at one and aim at the same time except on a bench. For my shooting it works but I don't get to shoot long range competition.
     
    Last edited: Oct 19, 2020
  17. d2wing

    d2wing Member

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    Well yes, that's why the cross hairs need to be level, otherwise you don't have a reference. It's easier to find a reference point looking through the scope that to insure your rifle is level.
     
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  18. d2wing

    d2wing Member

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    Reading my post I did not make it clear what I meant. Unless acted on by another force like wind. A bullet will always travel along a vertical plane from the bore since gravity is always straight down.. Assuming you are sighted at 100 yards, Since the scope is about the bore the bullet will be angled up when it leaves the bore and will travel in an arc along the vertical plane. The line of sight from the scope should be on that plane. In general the path of the bullet will rise along that plane and intersect the line of sight and then drop and cross again at the distance it is sighted in at 100 yards. Then continue to the target dropping along the plane and below the sight line. If the bore is to the left of the scope ( tilted or canted to the right) the bullet will rise from the left and rise above the line of sight to the left of the scope, It will intersect at the sighted in point but will continue moving right further away from the line of sight. And vice versa if you are canted left. Sighting further out will lessen the effect. The position of the scope lines are only correct when they are aligned with the bore and the vertical is straight up and down. I had a scoped 30-30 with an offset scope. In that case you allow for the offset when you sight it in. !/8 inch won't matter much in 200 yards as long as the scope is not canted. I hope this helps.
     
  19. WVRJ

    WVRJ Member

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    I ran into something like this a couple of weeks ago.I was shooting 3 of my rifles at 600 yards,and using the same bipod with all 3.Two of them have levels made into the rail,and I don't think they are true.I set the bipod legs to what I thought was level,and held into the wind what I felt would hit pretty close to POA.All 3 were about a foot to the right,which was the direction the wind would push the bullets.After that,I started reading about the impact cant has on where the bullet goes,and I was sure I was leaning the rifles several degrees.I went back and shot two of the rifles at 1,000 yards,but I was using my Wheeler level on the turrets to level the rifles,and holding into a very tricky wind as needed,and was making a 16 inch piece of steel go ding ding ding.One of the rifles is my 280AI that I built back in July,and it's very accurate,and it has a very nice optic on it.I put a clamp on level on the scope tube,$38 from Midway and sold by Burris.I leveled the crosshairs with a Wheeler level on the rail and clamped the other level on the barrel to use as a reference.All good until I put a plumb bob beside my 100 yard target to help get the clamp on level right.I put a level on the turret cap and it was off compared to the plumb bob by at least 5 degrees.I'm thinking either the level setup I use to mount scopes is wrong or the screws that hold the rail aren't true to the level of the action.This post is interesting,and I thank all of you for any info I can glean from this discussion.
     
  20. Picher

    Picher Member

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    I've recently theorized that the scope reticle doesn't need to be levelled, but the vertical wire needs to point to the center of the bore. Therefore, I rest the muzzle on the frame of my cellar window and, with the rifle bolt removed, rotate the scope in the mount so the vertical hair aligns with the bore. It takes about 10 seconds, as long as the scope mount is loose enough to turn, but not real loose. Should the scope turn as screws are tightened, loosen the screws and compensate for the turning, but most mounts have screws on both sides, so that shouldn't be a problem, provided screws are tightened equally on both sides. Thumb pressure across the scope/mount joint prevents rotation as the mount screws are incrementally tightened evenly. (It takes longer to read this than it takes to do the process.) :)
     
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  21. Walkalong

    Walkalong Moderator Staff Member

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    Well, a good scope will have the vertical part (wire/etched) pointed at the center of the bore if the horizontal part is level and the rifle is level, and of any decent quality.

    And vice versa, and the way I described above relies on that, since I am adjusting the scope so the vertical crosshair is parallel with the hanging string while leveling the rifle.

    So I am leveling the rifle, then making sure the recticle points straight down, and relying on the quality of my action so that line points to the center of the bore.
     
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