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  • Zeroing a rifle scope

    I have read a lot about zeroing my scope and in many explanations 100 yards is used as a example distance to zero a rifle scope. And in several discussions/ videos a drawing of the line of site of the scope intersecting with the 'highest' point in the bullet's trajectory at 100 yards (the zero distance) seems to me to be one of two scenarios. Isn't it possible (second scenario) that the line of site of the scope (if gun is stationary and reticle lowered more) could intersect the bullet's trajectory at two points ( A and B)? 'A' being a point along the bullet's ascent (before reaching its highest point along trajectory) and 'B' being a point along the bullet's descent? If so, in the first scenario, the gun would be zeroed at 100 yards, but in the second scenario it would be zeroed at a distance less than 100 yards and another distance farther than 100 yards. Am I understanding things wrong or am I presenting a valid point? If I'm correct, then the rule that a gun will always shoot 'low' if aimed at a target closer or further than the point of zero (100 yards in many explanations) would not always be true (if the second scenario applies). Right? Any advice would be appreciated.

  • #2
    In general you are right. A bullet's curved trajectory will normally cross the scope's line of sight twice, once on the rise and once again on the fall. Below is a good diagram showing a simple view of a bullet's path given a 200 yard zero. Note the the line of sight is not level.

    For normal hunting ranges the simple understanding of trajectory is sufficient. Long range shooting is a different story and has other factors that need consideration, such as wind drift..

    https://www.rifleshootermag.com/edit...-dummies/83897

    Last edited by PigHunter; 01-13-2020, 03:55 PM.
    Trump 2020 - Keep America Great!

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    • #3
      Due to the alignment of the rifle bore to the fixed sight plane of the scope, your bullet will indeed cross the horizontal plane twice.
      The 100 yard mark is a "zero" point. Not the "zero" rise in the bullets path. You gotta start somewhere.

      In all actuality, to (ahem!) "properly" sight in a scope, you should start at 25 yards.
      My .270 Win for example.
      At 25 yards, it will shoot dead on.
      At 100 yards, it will shoot dead on the vertical plane 1.5" above the horizontal plane.
      The bullet will actually continue to rise slightly, but very little. Not enough to make a difference in "point of impact" unless you're shooting aspirins.
      With a Sierra 130 grain SPBT bullet, my .270 Win, again crosses the horizontal plane, on the way down if you please, somewhere out around 250 to 260 yards.
      Drop from there out to 300 yards is minimal.
      With the light, fast .277 SPBT, out to about 250 to 275 yards, put the "+" where you want the bullet and squeeze.
      Dead deer!

      So, you are indeed correct, the bullet "should" cross "line-of-sight" twice.
      Once rising.
      Once falling.

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      • #4

        Some people will first zero a scope at 25yds and then move to 100yds (always shooting from a very stable platform). As the zeroed bullet passes the 100yd target it may rise some more or at some greater distance start to fall. The distance when it starts to fall it is called Maxium Point Blank Range for the benefit of hunters. That is the range the bullet starts to fall out of the vital kill zone. So, a hunter, when sighted in, can hold dead on out to that MPBR for a clean kill. Target shooting is a whole different thing.

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        • #5
          I was 30 years old when I got my first rifle. Being an engineer, I was consumed with learning all I could about ballistics and how to apply that to hunting. The Outdoor Life writer Jim Carmichael was one of my favorite sources of information. Here's a link to an interesting article of his concerning "The Perfect Zero"

          https://www.outdoorlife.com/articles.../perfect-zero/
          Trump 2020 - Keep America Great!

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          • #6
            I zero for a specific distance and learn my holds. Have never aimed center and just let stuff land in a zone.

            Never shot gap between sight pins in archery either. Yardage and hold point for a pin.

            Forces focus IMHO and focus helpa followthrough.

            YMMV
            ​​​​​​​

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            • #7
              The type of cartridge also is a factor. Some shoot flatter than others so the parabola is not as exaggerated.

              Most of us will zero a scope at 25 yards for the convenience factor. If the scope is way off, the gun may not even hit paper at 100 yards but it will be on the target somewhere at 25 yards. I get the scope adjusted reasonably close and then move out to 100 yards. Though I rarely shoot at anything further than 100 yards, I will have the scope of my 30-06 Springfield adjusted slightly high of bullseye centre at 100 yards so the bullet has dropped back in or very close to centre at 200 yards. The desired target on a wild animal is the "boiler room" (heart and lungs) which is a relatively big area for big game. With my scope set up that way I should be lethal shooting anything from deer to moose at ranges of 15 to 300 yards. I don't expect to be so accurate I can shoot them through the eye but they will be dead for certain nonetheless. As others have mentioned, shooting targets, especially competitively, is a different matter altogether. Boiler room mentality doesn't fit.

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              • #8
                At times I've been a center of mass kind of shooter. It all depends on the game, weapon, load, distance, running vs standing, etc. That's the advantage of using Jim Carmichael's method. I call B.S. on anyone who claims they can hit 1 MOA consistently in field conditions.

                To each their own.
                Trump 2020 - Keep America Great!

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                • #9
                  I grew up varmint hunting and had decent gear/ reloaded. Maybe has me going a diff direction than some, or maybe im just wandering around on my own.

                  When i shot 3d archery i went for exact yardage and shot for center of the kill. Never said " dunno what it is" and hold to stay in zone of bull.

                  Nope. Call it and shoot it for that.
                  Cost me more points when an error. But i usually won anyway.

                  No little x bullseye within kill back then. Everybody shot aluminum. Out to 60 yards. Was very good at judging yardage.

                  Interestingly, before archery i was good at yardage on varminting w rifles. Got good at 3d and my long range rifle yardage skills degraded.

                  ( Archery 0-60, rifles 0-450 )

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                  • #10
                    All have offered great advice. You are right, the bullet crosses the line of sight at two points. The faster the bullet, the flatter the trajectory. Whether you zero at 100 or 200 yards or Point Blank Range is completely arbitrary. Just choose one and learn how to shoot with the zero point you have chosen and you will be fine.

                    I zero all my rifles that shoot around 3000 fps and above at 200 yards. For hunting, most of my shots are under 250 yards so I can just aim at the center of the kill zone and shoot. I also shoot a lot out to 1000 yards and beyond and the same 200 yard zero point is used for all that. I simply plug 200 into the "zero range" parameter in my ballistics software and follow the holdover recommended by the software for a given range.

                    For lower velocity rifles like a 30-30 or .35 Rem. where hunting distance is normally under 100 yards (e.g. dense timber hunting) I zero for 100 yards.

                    The purpose for shooting first at 25 yards on a big sheet of paper is to get your bullet to impact somewhere on the paper with a randomly adjusted scope so you can dial the cross hair in until it is properly aligned on the target.

                    Zeroing process:
                    1. Bore sight at 25 yards if using a bolt action on a firm rest.
                    2. Zero about a quarter inch low at 25 yards.
                    3. Check zero at 100 yards and make minor adjustment if necessary.
                    4. If you desire a 200 yard zero, dial your scope "UP" 4 clicks and check zero at 200 yards. Adjust as necessary.

                    You can see what the expected drop is at more ranges by using a ballistics calculator like the one at jbmballistics.com
                    Last edited by DakotaMan; 01-14-2020, 06:12 PM.

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