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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Anyone using the Horus Reticle?
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<blockquote data-quote="bruce_ventura" data-source="post: 592813" data-attributes="member: 34084"><p>That surprises me too, because the ballistic drop changes you cite are way too low. Obviously, with these ballistic drop values, you would (incorrectly) conclude that a BDC reticle is more accurate than it is. You have to use the JBM website software carefully to avoid erroneous results. </p><p> </p><p>Go back and try a trajectory calculation with these settings (<a href="http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi" target="_blank">JBM - Calculations - Trajectory</a>): </p><p>Select this bullet from the library:</p><p>Sierra, 0.308 cal, 168 gr, HPBT MatchKing™</p><p>Enter these values: </p><p>Muzzle Velocity: 2650 fps</p><p>Distance to Chrono: 10 ft</p><p>Zero for the next eight boxes (sight height - cant angle)</p><p>Wind and target values should not matter</p><p>Plot results from 0-700 yds. </p><p>Zero range: 100 ft (but it will be ignored due the settings at the bottom of the page)</p><p>Temp: 80 F</p><p>Pressure 29.92 in Hg</p><p>Humidity: 78% (changing this value has almost no effect)</p><p>Altitude: 5,000 ft</p><p><strong>Uncheck box that says "Std atmosphere at altitude".</strong></p><p><strong>Check the box that says "Pressure is corrected"</strong></p><p>Use default values for next two boxes.</p><p>Column 1: 1 inch. Column 2: 1 MOA</p><p><strong>Uncheck all the boxes at the bottom of the page.</strong></p><p> </p><p>Click the calculate button. You should get something like this:</p><p><span style="font-family: 'Times New Roman'">Trajectory </span></p><p><span style="font-family: 'Times New Roman'">Input Data </span></p><p><span style="font-family: 'Times New Roman'">Manufacturer: </span><span style="font-family: 'Times New Roman'">Sierra </span></p><p><span style="font-family: 'Times New Roman'">Description: </span><span style="font-family: 'Times New Roman'">HPBT MatchKing™ </span></p><p><span style="font-family: 'Times New Roman'">Caliber: </span><span style="font-family: 'Times New Roman'">0.308 in </span></p><p><span style="font-family: 'Times New Roman'">Weight: </span><span style="font-family: 'Times New Roman'">168.0 gr </span></p><p><span style="font-family: 'Times New Roman'">Ballistic Coefficients: </span><span style="font-family: 'Times New Roman'">0.405 [0-1600], 0.424 [1600-2100], 0.447 [2100-2600], 0.462 [2600-5000] G1 </span></p><p><span style="font-family: 'Times New Roman'">Muzzle Velocity: </span><span style="font-family: 'Times New Roman'">2650.0 ft/s </span></p><p><span style="font-family: 'Times New Roman'">Distance to Chronograph: </span><span style="font-family: 'Times New Roman'">10.0 ft </span></p><p><span style="font-family: 'Times New Roman'">Sight Height: </span><span style="font-family: 'Times New Roman'">0.00 in </span></p><p><span style="font-family: 'Times New Roman'">Sight Offset: </span><span style="font-family: 'Times New Roman'">0.00 in </span></p><p><span style="font-family: 'Times New Roman'">Zero Height: </span><span style="font-family: 'Times New Roman'">0.00 in </span></p><p><span style="font-family: 'Times New Roman'">Zero Offset: </span><span style="font-family: 'Times New Roman'">0.00 in </span></p><p><span style="font-family: 'Times New Roman'">Windage: </span><span style="font-family: 'Times New Roman'">0.000 MOA </span></p><p><span style="font-family: 'Times New Roman'">Elevation: </span><span style="font-family: 'Times New Roman'">0.000 MOA </span></p><p><span style="font-family: 'Times New Roman'">Line Of Sight Angle: </span><span style="font-family: 'Times New Roman'">0.0 deg </span></p><p><span style="font-family: 'Times New Roman'">Cant Angle: </span><span style="font-family: 'Times New Roman'">0.0 deg </span></p><p><span style="font-family: 'Times New Roman'">Wind Speed: </span><span style="font-family: 'Times New Roman'">10.0 mph </span></p><p><span style="font-family: 'Times New Roman'">Wind Angle: </span><span style="font-family: 'Times New Roman'">0.0 deg </span></p><p><span style="font-family: 'Times New Roman'">Target Speed: </span><span style="font-family: 'Times New Roman'">10.0 mph </span></p><p><span style="font-family: 'Times New Roman'">Target Angle: </span><span style="font-family: 'Times New Roman'">90.0 deg </span></p><p><span style="font-family: 'Times New Roman'">Target Height: </span><span style="font-family: 'Times New Roman'">12.0 in </span></p><p><span style="font-family: 'Times New Roman'">Temperature: </span><span style="font-family: 'Times New Roman'">80.0 °F </span></p><p><span style="font-family: 'Times New Roman'">Pressure: </span><span style="font-family: 'Times New Roman'">29.92 in Hg </span></p><p><span style="font-family: 'Times New Roman'">Humidity: </span><span style="font-family: 'Times New Roman'">78.0 % </span></p><p><span style="font-family: 'Times New Roman'">Altitude: </span><span style="font-family: 'Times New Roman'">5000.0 ft </span></p><p><span style="font-family: 'Times New Roman'">Vital Zone Radius: 5</span><span style="font-family: 'Times New Roman'">.0 in </span></p><p><span style="font-family: 'Times New Roman'">Std. Atmosphere at Altitude: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Pressure is Corrected: </span><span style="font-family: 'Times New Roman'">Yes </span></p><p><span style="font-family: 'Times New Roman'">Zero at Max. Point Blank Range: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Target Relative Drops: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Mark Sound Barrier Crossing: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Include Extra Rows: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Column 1 Units: </span><span style="font-family: 'Times New Roman'">1.00 in </span></p><p><span style="font-family: 'Times New Roman'">Column 2 Units: </span><span style="font-family: 'Times New Roman'">1.00 MOA </span></p><p><span style="font-family: 'Times New Roman'">Round Output to Whole Numbers: </span><span style="font-family: 'Times New Roman'">No </span></p><p><span style="font-family: 'Times New Roman'">Output Data </span><span style="font-family: 'Times New Roman'">Elevation: </span><span style="font-family: 'Times New Roman'">0.000 MOA </span></p><p><span style="font-family: 'Times New Roman'">Windage: </span><span style="font-family: 'Times New Roman'">0.000 MOA </span></p><p><span style="font-family: 'Times New Roman'">Atmospheric Density: </span><span style="font-family: 'Times New Roman'">0.06040 lb/ft³ </span></p><p><span style="font-family: 'Times New Roman'">Speed of Sound: </span><span style="font-family: 'Times New Roman'">1138.9 ft/s </span></p><p><span style="font-family: 'Times New Roman'">Maximum PBR: </span><span style="font-family: 'Times New Roman'">313 yd </span></p><p><span style="font-family: 'Times New Roman'">Maximum PBR Zero: </span><span style="font-family: 'Times New Roman'">262 yd </span></p><p><span style="font-family: 'Times New Roman'">Range of Maximum Height: </span><span style="font-family: 'Times New Roman'">135 yd </span></p><p><span style="font-family: 'Times New Roman'">Energy at Maximum PBR: </span><span style="font-family: 'Times New Roman'">1763.8 ft•lbs </span></p><p><span style="font-family: 'Times New Roman'">Sectional Density: </span><span style="font-family: 'Times New Roman'">0.253 lb/in² </span></p><p> </p><p><span style="font-family: 'Times New Roman'">Calculated Table </span></p><div style="text-align: left"><strong><span style="font-family: 'Times New Roman'">Range </span></strong><strong><span style="font-family: 'Times New Roman'">Drop </span></strong><strong><span style="font-family: 'Times New Roman'">Drop </span></strong></div> <div style="text-align: left"><strong><span style="font-family: 'Times New Roman'">(yd) </span></strong><strong><span style="font-family: 'Times New Roman'">(in) </span></strong><strong><span style="font-family: 'Times New Roman'">(MOA) </span></strong></div><p><span style="font-family: 'Times New Roman'">0 </span><span style="font-family: 'Times New Roman'">0.0 </span><span style="font-family: 'Times New Roman'">***</span></p><p><span style="font-family: 'Times New Roman'">100 </span><span style="font-family: 'Times New Roman'">-2.6 </span><span style="font-family: 'Times New Roman'">-2.5</span></p><p><span style="font-family: 'Times New Roman'">200 </span><span style="font-family: 'Times New Roman'">-10.7 </span><span style="font-family: 'Times New Roman'">-5.1</span></p><p><span style="font-family: 'Times New Roman'">300 </span><span style="font-family: 'Times New Roman'">-25.2 </span><span style="font-family: 'Times New Roman'">-8.0</span></p><p><span style="font-family: 'Times New Roman'">400 </span><span style="font-family: 'Times New Roman'">-46.9 </span><span style="font-family: 'Times New Roman'">-11.2</span></p><p><span style="font-family: 'Times New Roman'">500 </span><span style="font-family: 'Times New Roman'">-77.0 </span><span style="font-family: 'Times New Roman'">-14.7</span></p><p><span style="font-family: 'Times New Roman'">600 </span><span style="font-family: 'Times New Roman'">-116.6 </span><span style="font-family: 'Times New Roman'">-18.6</span></p><p><span style="font-family: 'Times New Roman'">700 </span><span style="font-family: 'Times New Roman'">-167.5 </span><span style="font-family: 'Times New Roman'">-22.8</span></p><p> </p><p>I only showed the first three columns of calculations. Bullet drop at 700 yds is -167.5" (-22.8 MOA). </p><p> </p><p>Now repeat the calculation, changing only temp and altitude values as shown:</p><p>Temp: 80F and Altitude: 10,000 ft. -> Bullet drop at 700 yds is -157.0" (-21.4 MOA).</p><p>Temp: 15F and Altitude: 5,000 ft. -> Bullet drop at 700 yds is -175.4" (-23.9 MOA).</p><p> </p><p>Do the math and you find that increasing altitude raises the point of impact by 10.4" (1.4 MOA). </p><p>Likewise, decreasing temperature lowers the point of impact by 7.09" (1.1 MOA). </p><p> </p><p>These single parameter effects make sense when you think in terms of changes in air density and bullet drag. When you start combining the major effects (altitude, barometric pressure, temperature and line of sight angle (uphill/downhill)), you find that they can add up to some pretty large shifts in the point of impact. The BDC knob approach ignores all these environmental effects. Easy to use? Yes. Accurate at long range? Not so much.</p></blockquote><p></p>
[QUOTE="bruce_ventura, post: 592813, member: 34084"] That surprises me too, because the ballistic drop changes you cite are way too low. Obviously, with these ballistic drop values, you would (incorrectly) conclude that a BDC reticle is more accurate than it is. You have to use the JBM website software carefully to avoid erroneous results. Go back and try a trajectory calculation with these settings ([URL="http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi"]JBM - Calculations - Trajectory[/URL]): Select this bullet from the library: Sierra, 0.308 cal, 168 gr, HPBT MatchKing™ Enter these values: Muzzle Velocity: 2650 fps Distance to Chrono: 10 ft Zero for the next eight boxes (sight height - cant angle) Wind and target values should not matter Plot results from 0-700 yds. Zero range: 100 ft (but it will be ignored due the settings at the bottom of the page) Temp: 80 F Pressure 29.92 in Hg Humidity: 78% (changing this value has almost no effect) Altitude: 5,000 ft [B]Uncheck box that says "Std atmosphere at altitude".[/B] [B]Check the box that says "Pressure is corrected"[/B] Use default values for next two boxes. Column 1: 1 inch. Column 2: 1 MOA [B]Uncheck all the boxes at the bottom of the page.[/B] Click the calculate button. You should get something like this: [FONT=Times New Roman]Trajectory [/FONT] [FONT=Times New Roman]Input Data [/FONT] [FONT=Times New Roman]Manufacturer: [/FONT][FONT=Times New Roman]Sierra [/FONT] [FONT=Times New Roman]Description: [/FONT][FONT=Times New Roman]HPBT MatchKing™ [/FONT] [FONT=Times New Roman]Caliber: [/FONT][FONT=Times New Roman]0.308 in [/FONT] [FONT=Times New Roman]Weight: [/FONT][FONT=Times New Roman]168.0 gr [/FONT] [FONT=Times New Roman]Ballistic Coefficients: [/FONT][FONT=Times New Roman]0.405 [0-1600], 0.424 [1600-2100], 0.447 [2100-2600], 0.462 [2600-5000] G1 [/FONT] [FONT=Times New Roman]Muzzle Velocity: [/FONT][FONT=Times New Roman]2650.0 ft/s [/FONT] [FONT=Times New Roman]Distance to Chronograph: [/FONT][FONT=Times New Roman]10.0 ft [/FONT] [FONT=Times New Roman]Sight Height: [/FONT][FONT=Times New Roman]0.00 in [/FONT] [FONT=Times New Roman]Sight Offset: [/FONT][FONT=Times New Roman]0.00 in [/FONT] [FONT=Times New Roman]Zero Height: [/FONT][FONT=Times New Roman]0.00 in [/FONT] [FONT=Times New Roman]Zero Offset: [/FONT][FONT=Times New Roman]0.00 in [/FONT] [FONT=Times New Roman]Windage: [/FONT][FONT=Times New Roman]0.000 MOA [/FONT] [FONT=Times New Roman]Elevation: [/FONT][FONT=Times New Roman]0.000 MOA [/FONT] [FONT=Times New Roman]Line Of Sight Angle: [/FONT][FONT=Times New Roman]0.0 deg [/FONT] [FONT=Times New Roman]Cant Angle: [/FONT][FONT=Times New Roman]0.0 deg [/FONT] [FONT=Times New Roman]Wind Speed: [/FONT][FONT=Times New Roman]10.0 mph [/FONT] [FONT=Times New Roman]Wind Angle: [/FONT][FONT=Times New Roman]0.0 deg [/FONT] [FONT=Times New Roman]Target Speed: [/FONT][FONT=Times New Roman]10.0 mph [/FONT] [FONT=Times New Roman]Target Angle: [/FONT][FONT=Times New Roman]90.0 deg [/FONT] [FONT=Times New Roman]Target Height: [/FONT][FONT=Times New Roman]12.0 in [/FONT] [FONT=Times New Roman]Temperature: [/FONT][FONT=Times New Roman]80.0 °F [/FONT] [FONT=Times New Roman]Pressure: [/FONT][FONT=Times New Roman]29.92 in Hg [/FONT] [FONT=Times New Roman]Humidity: [/FONT][FONT=Times New Roman]78.0 % [/FONT] [FONT=Times New Roman]Altitude: [/FONT][FONT=Times New Roman]5000.0 ft [/FONT] [FONT=Times New Roman]Vital Zone Radius: 5[/FONT][FONT=Times New Roman].0 in [/FONT] [FONT=Times New Roman]Std. Atmosphere at Altitude: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Pressure is Corrected: [/FONT][FONT=Times New Roman]Yes [/FONT] [FONT=Times New Roman]Zero at Max. Point Blank Range: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Target Relative Drops: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Mark Sound Barrier Crossing: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Include Extra Rows: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Column 1 Units: [/FONT][FONT=Times New Roman]1.00 in [/FONT] [FONT=Times New Roman]Column 2 Units: [/FONT][FONT=Times New Roman]1.00 MOA [/FONT] [FONT=Times New Roman]Round Output to Whole Numbers: [/FONT][FONT=Times New Roman]No [/FONT] [FONT=Times New Roman]Output Data [/FONT][FONT=Times New Roman]Elevation: [/FONT][FONT=Times New Roman]0.000 MOA [/FONT] [FONT=Times New Roman]Windage: [/FONT][FONT=Times New Roman]0.000 MOA [/FONT] [FONT=Times New Roman]Atmospheric Density: [/FONT][FONT=Times New Roman]0.06040 lb/ft³ [/FONT] [FONT=Times New Roman]Speed of Sound: [/FONT][FONT=Times New Roman]1138.9 ft/s [/FONT] [FONT=Times New Roman]Maximum PBR: [/FONT][FONT=Times New Roman]313 yd [/FONT] [FONT=Times New Roman]Maximum PBR Zero: [/FONT][FONT=Times New Roman]262 yd [/FONT] [FONT=Times New Roman]Range of Maximum Height: [/FONT][FONT=Times New Roman]135 yd [/FONT] [FONT=Times New Roman]Energy at Maximum PBR: [/FONT][FONT=Times New Roman]1763.8 ft•lbs [/FONT] [FONT=Times New Roman]Sectional Density: [/FONT][FONT=Times New Roman]0.253 lb/in² [/FONT] [FONT=Times New Roman]Calculated Table [/FONT] [LEFT][B][FONT=Times New Roman]Range [/FONT][/B][B][FONT=Times New Roman]Drop [/FONT][/B][B][FONT=Times New Roman]Drop [/FONT][/B] [B][FONT=Times New Roman](yd) [/FONT][/B][B][FONT=Times New Roman](in) [/FONT][/B][B][FONT=Times New Roman](MOA) [/FONT][/B][/LEFT] [FONT=Times New Roman]0 [/FONT][FONT=Times New Roman]0.0 [/FONT][FONT=Times New Roman]***[/FONT] [FONT=Times New Roman]100 [/FONT][FONT=Times New Roman]-2.6 [/FONT][FONT=Times New Roman]-2.5[/FONT] [FONT=Times New Roman]200 [/FONT][FONT=Times New Roman]-10.7 [/FONT][FONT=Times New Roman]-5.1[/FONT] [FONT=Times New Roman]300 [/FONT][FONT=Times New Roman]-25.2 [/FONT][FONT=Times New Roman]-8.0[/FONT] [FONT=Times New Roman]400 [/FONT][FONT=Times New Roman]-46.9 [/FONT][FONT=Times New Roman]-11.2[/FONT] [FONT=Times New Roman]500 [/FONT][FONT=Times New Roman]-77.0 [/FONT][FONT=Times New Roman]-14.7[/FONT] [FONT=Times New Roman]600 [/FONT][FONT=Times New Roman]-116.6 [/FONT][FONT=Times New Roman]-18.6[/FONT] [FONT=Times New Roman]700 [/FONT][FONT=Times New Roman]-167.5 [/FONT][FONT=Times New Roman]-22.8[/FONT] I only showed the first three columns of calculations. Bullet drop at 700 yds is -167.5" (-22.8 MOA). Now repeat the calculation, changing only temp and altitude values as shown: Temp: 80F and Altitude: 10,000 ft. -> Bullet drop at 700 yds is -157.0" (-21.4 MOA). Temp: 15F and Altitude: 5,000 ft. -> Bullet drop at 700 yds is -175.4" (-23.9 MOA). Do the math and you find that increasing altitude raises the point of impact by 10.4" (1.4 MOA). Likewise, decreasing temperature lowers the point of impact by 7.09" (1.1 MOA). These single parameter effects make sense when you think in terms of changes in air density and bullet drag. When you start combining the major effects (altitude, barometric pressure, temperature and line of sight angle (uphill/downhill)), you find that they can add up to some pretty large shifts in the point of impact. The BDC knob approach ignores all these environmental effects. Easy to use? Yes. Accurate at long range? Not so much. [/QUOTE]
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