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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Brunton 3x9x40 BDC reticle question
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<blockquote data-quote="pandjbox" data-source="post: 1021253" data-attributes="member: 86112"><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px">Thanks much for pointing out the article by Barsness on the Eterna.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">It does, however, leave me with more that I can't explain.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">Let me summarize what I think I know.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">1) The Eterna literature shows bar values of 3.5, 11.5, and 23.5 MOA</span></span></p><p> </p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px">(a jpeg picture would be here if I knew how to create it as a URL. I would be glad to send it as an email attachment if you would like to provide an email address)</span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p> </p><p> </p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span><span style="font-size: 12px"> </span> </span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px">2)</span><span style="font-size: 12px"> </span><span style="font-size: 12px">The Bar values are consistent with the values I measure for my Echo scope and a side by side comparison with the Eterna and Echo looking at the same object.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">3)</span><span style="font-size: 12px"> </span><span style="font-size: 12px">My measurement of the first Echo Bar value is consistent with a side by side comparison with my Leupold 3x9x40 VII with a spec value for the distance from the top of the broad part of the lower post to the crosshair of a 3.1 MOA.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">Based on range experience (the Leupold is on a 300wm) out to 500yds and an elk kill at 525yds, I believe Leopold spec value.</span><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p> </p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-size: 12px"><span style="font-family: 'Calibri'">From the Echo literature</span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p> </p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">For example: A 30-06, shooting a 168 grain Sierra Match King with a muzzle velocity </span></span></span><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">of 2700 fps would have the following ballistic drop.</span></span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">Vertical Sight Reference Distance Estimated Drop</span></span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">Sight-in (Main Cross-Hair) 200 Yards 0 "</span></span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">Bar Number 1 300 Yards -3.5"</span></span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">Bar Number 2 400 Yards -24"</span></span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">Bar Number 3 500 Yards -48"</span></span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-size: 12px"><span style="font-family: 'Calibri'">This is assuming the rifle scope was "Zeroed" at 200 yards.</span></span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-family: 'Calibri'"><span style="font-size: 12px">This implies (I think) MOA values of approx. 1.2, 6, and 9.</span><span style="font-size: 12px"> </span> <span style="font-size: 12px">When I run the above bullet parameters through the online JBM ballistics calculator, drops at 300, 400 and 500yds are 8.6, 25, and 50.9in.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">So I'd give Bar 2 and 3 a "consistent" grade but not Bar 1.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">When I run the above bullet parameters through the Brunton calculator which gives the distance when the bullet crosses each Bar but not the value of the drop below LOS, it gives distance values of 247, 307, and 372 yds for Bars 1, 2, and 3.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">This is very consistent with the Barsness article but very inconsistent with the Brunton Echo literature.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">And when I look at the MOA values for the 247, 307 and 372yds from the JBM calculator I get approx. an MOA of 1.3, 2.7. and 6 which is inconsistent with the Echo literature and very much with my measurements.</span><span style="font-size: 12px"> </span></span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p> </p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p><p><span style="font-family: 'Myriad-Roman'"><span style="font-family: 'Calibri'"><span style="font-size: 12px">So the conclusions I'm coming to are that the Brunton calculator has the wrong MOA values in it for the bars (which a Brunton representative essentially admitted) and at some point the BDC MOA design values changed.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">I'd be very interested in hearing your assessment.</span><span style="font-size: 12px"> </span><span style="font-size: 12px">Sorry for the almost OCD response but as a physicist, engineer and avid hunter I am somewhat perplexed. </span> </span></span></p><p><span style="font-family: 'Times New Roman'"><span style="font-size: 12px"> </span></span></p></blockquote><p></p>
[QUOTE="pandjbox, post: 1021253, member: 86112"] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Calibri][SIZE=3]Thanks much for pointing out the article by Barsness on the Eterna.[/SIZE][SIZE=3] [/SIZE][SIZE=3]It does, however, leave me with more that I can’t explain.[/SIZE][SIZE=3] [/SIZE][SIZE=3]Let me summarize what I think I know.[/SIZE][SIZE=3] [/SIZE][SIZE=3]1) The Eterna literature shows bar values of 3.5, 11.5, and 23.5 MOA[/SIZE][/FONT] [FONT=Calibri][SIZE=3][/SIZE][/FONT] [FONT=Calibri][SIZE=3](a jpeg picture would be here if I knew how to create it as a URL. I would be glad to send it as an email attachment if you would like to provide an email address)[/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Calibri][SIZE=3][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3][/SIZE][/FONT] [FONT=Calibri][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][/FONT] [FONT=Calibri][SIZE=3]2)[/SIZE][SIZE=3] [/SIZE][SIZE=3]The Bar values are consistent with the values I measure for my Echo scope and a side by side comparison with the Eterna and Echo looking at the same object.[/SIZE][SIZE=3] [/SIZE][SIZE=3]3)[/SIZE][SIZE=3] [/SIZE][SIZE=3]My measurement of the first Echo Bar value is consistent with a side by side comparison with my Leupold 3x9x40 VII with a spec value for the distance from the top of the broad part of the lower post to the crosshair of a 3.1 MOA.[/SIZE][SIZE=3] [/SIZE][SIZE=3]Based on range experience (the Leupold is on a 300wm) out to 500yds and an elk kill at 525yds, I believe Leopold spec value.[/SIZE][SIZE=3] [/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Calibri][SIZE=3] [/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [SIZE=3][FONT=Calibri]From the Echo literature[/FONT][/SIZE] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Calibri][SIZE=3] [/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]For example: A 30-06, shooting a 168 grain Sierra Match King with a muzzle velocity [/FONT][/SIZE][/FONT][FONT=Myriad-Roman][SIZE=3][FONT=Calibri]of 2700 fps would have the following ballistic drop.[/FONT][/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]Vertical Sight Reference Distance Estimated Drop[/FONT][/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]Sight-in (Main Cross-Hair) 200 Yards 0 “[/FONT][/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]Bar Number 1 300 Yards -3.5”[/FONT][/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]Bar Number 2 400 Yards -24”[/FONT][/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]Bar Number 3 500 Yards -48”[/FONT][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Myriad-Roman][SIZE=3][FONT=Calibri]This is assuming the rifle scope was “Zeroed” at 200 yards.[/FONT][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Myriad-Roman][FONT=Calibri][SIZE=3]This implies (I think) MOA values of approx. 1.2, 6, and 9.[/SIZE][SIZE=3] [/SIZE][SIZE=3] [/SIZE][SIZE=3]When I run the above bullet parameters through the online JBM ballistics calculator, drops at 300, 400 and 500yds are 8.6, 25, and 50.9in.[/SIZE][SIZE=3] [/SIZE][SIZE=3]So I’d give Bar 2 and 3 a “consistent” grade but not Bar 1.[/SIZE][SIZE=3] [/SIZE][SIZE=3]When I run the above bullet parameters through the Brunton calculator which gives the distance when the bullet crosses each Bar but not the value of the drop below LOS, it gives distance values of 247, 307, and 372 yds for Bars 1, 2, and 3.[/SIZE][SIZE=3] [/SIZE][SIZE=3]This is very consistent with the Barsness article but very inconsistent with the Brunton Echo literature.[/SIZE][SIZE=3] [/SIZE][SIZE=3]And when I look at the MOA values for the 247, 307 and 372yds from the JBM calculator I get approx. an MOA of 1.3, 2.7. and 6 which is inconsistent with the Echo literature and very much with my measurements.[/SIZE][SIZE=3] [/SIZE][/FONT][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Myriad-Roman][FONT=Calibri][SIZE=3] [/SIZE][/FONT][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [FONT=Myriad-Roman][FONT=Calibri][SIZE=3]So the conclusions I’m coming to are that the Brunton calculator has the wrong MOA values in it for the bars (which a Brunton representative essentially admitted) and at some point the BDC MOA design values changed.[/SIZE][SIZE=3] [/SIZE][SIZE=3]I’d be very interested in hearing your assessment.[/SIZE][SIZE=3] [/SIZE][SIZE=3]Sorry for the almost OCD response but as a physicist, engineer and avid hunter I am somewhat perplexed. [/SIZE][SIZE=3] [/SIZE][/FONT][/FONT] [FONT=Times New Roman][SIZE=3] [/SIZE][/FONT] [/QUOTE]
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