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I am confused. A recent issue of F&S says that at 300 yards a 270. shot will be 9 inches low if zeroed at 100. The same issue

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  • I am confused. A recent issue of F&S says that at 300 yards a 270. shot will be 9 inches low if zeroed at 100. The same issue

    I am confused. A recent issue of F&S; says that at 300 yards a 270. shot will be 9 inches low if zeroed at 100. The same issue says that if you zeroe the rifle 3 inches high at 100 yards it will be on center at 300 yards. Woudlnt theat make it 6 inches low if the first statement is true. Please explain. If you want to see it it is in the accuracy issue on the page about hao to make a person shoot better and trajectory etc. Thanks

  • #2
    bullets trajectories arc. If it was a straight line you'd be right about the 6 inches low.

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    • #3
      steve is right about bullet arc but I think you read something wrong. 3 inches high at 100 will not equal dead on at 300. Not with 270 Win. It's best to do the testing yourself with Your rifle. I'll admit it's tough to find a range that has 300 yd targets unless it's a club.

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      • #4
        This is about right. You'll get trajectory like this if you zero at 25 yards or so. It's not exact, but you are just about set to hold dead on on deer or bigger size game anywhere from 0-300 yards.

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        • #5
          Was this article about "maximum point blank" maybe?

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          • #6
            No, take a look for yourself, it was saying that at 300 yards a 270 WSM would hit dead center if 3 inches high at 100 yards. Lowere on the page it said a 270 WSM would drop 9 inches at 300 yards if zeroed at 100. Takea look. It is the end of the acurracy revolution article by David Petzal. Maybe in a July issue. Dont quote but i cant remember it exactly.

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            • #7
              If sighted dead on at 100 yards the bullet will fall 9 inches at the 300 yard mark. If the bullet is sighted to strike 3 inches above point of aim at 100 the resulting trajectory will place the round on target (or pretty close) at 300 yards. The trajectory of a rifle shot is arched. By sighting it 3 inches high at 100 yards we "adjust" the arc to hit our target at point of aim at 300 yards.

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              • #8
                270 with Hornady 140 grain SST at 2940 fps

                Muzzle -1.5
                50 yards 1.7
                100 Yards 3.8
                200 yards 4.5
                300 yards 0.0
                400 yards -10.6
                500 yards -28.2

                I sight all my rifle in at 200 yards then I tweak them to the way I use my aim point and hold over. Sounds confusing but it works for me!

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                • #9
                  its possible that they had diff bullets. or they suck at math.

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                  • #10
                    It's close enough, perhaps they rounded the numbers off to not to cornfuze some people!

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                    • #11
                      Sorry Clay, but 6 inches isnt rounding though Bee Keepers answer sounds relativily plausible.

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                      • #12
                        I agree with Beekeeper and Clay. DEP is probably rounding a bit. Using a fast (3,200+ fps) 130 gr high ballistic coefficient bullet +3 at 100 yards is about right to zero at 300 yards. This is from referencing long range trajectory tables. Even Clay's 140 gr Hornady is less than 4" at 100 to zero at 400. DEP is just making a point. As Jim says, have to check with each gun and load. I'll add location - depends on altitude, too.

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                        • #13
                          KMB33 – just realized there still might be some head scratching since you mentioned a 6” difference. Forgive me if I say something you already understand but perhaps this will help others.

                          So, why does only +3” at 100 yards raise the point of impact 9” at 300 yards? Basically, small changes closer to the muzzle make big changes downrange.

                          The bullet follows an arcing trajectory, actually a path with a decreasing radius. As soon as a bullet leaves the muzzle, gravity starts accelerating it downward. Drag from the atmosphere slows the bullet down allowing even more time for gravity to act on the bullet. If you look at the trajectory from the side the bullet looks like it is curving downward. The curve gets “steeper” the further from the muzzle.

                          Imagine a straight sight line from the muzzle to bulls-eyes at 100 and 300 yards. If you aligned the barrel with this line and fired directly at the target, the bullet will hit below the 100 yard bulls-eye and even further below the 300. To zero at 100 yards the barrel has to be pointed slightly upward. The bullet rises, peaks, and starts to fall, crossing the sight line right at 100 yards. To zero at 300 yards, you have to point the barrel even further skyward.

                          With a scope the muzzle is actually 1.5” or so below the sight line. Data using a -1.5” muzzle suggests sighting in a bit over 3” high at 100 yards for a 300 yard zero. Simplistically, going from a 100 yard zero to a 300 yard zero, the factor relating the rise at 100 yards to that at 300 yards is 3. So +3” at 100 yards results in +9” at 300 yards (3x3”=9”).

                          Perhaps the best way to grasp this is to plot various trajectories on graph paper (if they still make the stuff), or use the charting feature in a spreadsheet program like MS Exel. You can calculate the points using a free online ballistics program such as JBM (plot in 10 or 25 yard increments out to 300 yards). Some ballistics programs might even plot the graphs for you. The ballistics programs just give estimates – still have to actually shoot each gun at the range to get real world results.

                          I hope this is makes some sense and helps – just got back from watching the Red Wings crush the Penguins 5-0 (Go Wings!) and my head was clearer before I got there. Someone might want to check my logic while I get an aspirin.

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                          • #14
                            thanks MLH, it suddenly makes sense. So the bullet is like a thrown fooball, so the higher up you aim the football the farther it will go. Thanks.

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                            • #15
                              MOP!

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