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That can't be right!

Old 10-09-2021, 01:59 PM
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Default That can't be right!

Or so I thought. I made up a dope sheet for my 6.5 CM with 143 gr Hornady ELD-X bullets with a MV of 2640. I printed it out and at 700 yards it said to come up 18.5 MOA -NO WAY! Then I looked at the drop and it was 135". A bit of calculation (7 x 1.05= 7.35; 135/7.35=18.3). Hmmm....well I'll be darned it is right. Now this is only an approximation and my actual dope sheet will likely be different but at least it gets me in the ball park. No wonder the higher class scopes have a zero stop. It could be very easy to forget.
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Old 10-10-2021, 08:16 AM
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did you shoot it yet to see if your trajectory matches your chart?
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Old 10-10-2021, 11:56 AM
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Sounds about right - 5.3 mils at 700... my Dasher was 4.7mils on a 700yrds target used on one of the stages yesterday.

“Weaponized math,” “ballistics,” “trajectory,” “projectile physics,” what have you... it’s actually a lot of fun.

Really fun when you look at a time of flight table for your rounds... it’s not so uncommon to send bullets within a relatively easily managed trajectory on a 2-3 second flight. A lot of folks don’t realize just how long it takes for bullets to travel, so it’s exceptionally common during long range classes or competition matches when a new shooter is poised to spot impacts, they’ll call a miss (“no call,” or “re-engage”, or “next target,”) then immediately have to stumble it back and call “impact!”. Getting out to 1200+, a guy can cycle the bolt and be back on target before the first bullet arrives!
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Old 10-10-2021, 03:58 PM
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Originally Posted by Ridge Runner View Post
did you shoot it yet to see if your trajectory matches your chart?
No RR not yet. Like I said I won't take this as gospel. But it will likely get me in the ball park and I can tweak it to match my load exactly.
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Old 10-10-2021, 06:15 PM
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If you know your BC and a true velocity, StrelokPro, AB Mobile, or Hornady 4DoF will have you within two clicks at 700 yards. 18.5moa is pretty close to making sense for that load.

Running it through Hornady 4DoF and StrelokPro, I get 18moa at 1000ft DA (not actual elevation, DA) out of both calculators, so 18.5 would have to be very low elevation, as in negative 1500ft density altitude. I’ve shot in negative DA’s, but never -1500ft. But like I mentioned, these proven calculators will have you within 2 clicks, half MOA, so a discrepancy between yours and mine of 5” at 700 isn’t so surprising (or maybe you really are shooting -1500ft DA?).
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Old 10-10-2021, 07:57 PM
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Originally Posted by Nomercy448 View Post
If you know your BC and a true velocity, StrelokPro, AB Mobile, or Hornady 4DoF will have you within two clicks at 700 yards. 18.5moa is pretty close to making sense for that load.

Running it through Hornady 4DoF and StrelokPro, I get 18moa at 1000ft DA (not actual elevation, DA) out of both calculators, so 18.5 would have to be very low elevation, as in negative 1500ft density altitude. I’ve shot in negative DA’s, but never -1500ft. But like I mentioned, these proven calculators will have you within 2 clicks, half MOA, so a discrepancy between yours and mine of 5” at 700 isn’t so surprising (or maybe you really are shooting -1500ft DA?).
my elevation here is between 1300 and 2000 ft. Not sure what DA means and definitely don't know what a-day is!? My BC according to Hornady is .625 and my MV is 2640
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Old 10-10-2021, 11:27 PM
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Originally Posted by bronko22000 View Post
my elevation here is between 1300 and 2000 ft. Not sure what DA means and definitely don't know what a-day is!? My BC according to Hornady is .625 and my MV is 2640
DA is Density Altitude. In a nutshell, it’s a singular compilation of Altitude, Barometric Pressure, Humidity, and Temperature - effectively a one stop shop for “environmental conditions” which inputs one number to correspond to a relevant air density.

In other words, it’s a way of saying what altitude the atmosphere currently “acting like”. So I might be shooting at 1300ft physical elevation at my home range, but if it’s cool and damp in the morning, the air will be thicker than normal, so it’s “acting like” I’m at 700ft instead of 1300. Alternatively, on a hot and dry afternoon, the air might be super thin, and “acting like” 4500ft, even though I’m still only physically at 1300ft elevation. So we put in ONE number into our ballistic calculators.

Negative DA’s are largely an imaginary construct - there ARE dry land locations around the world which literally sit below sea level, but not many, and really not many very far below Sea Level in the US. But it isn’t so uncommon for cold, damp mornings even here at 1300ft to yield -500ft DA a few times per year.

With that bullet, you’ll also be more accurate in calculating downrange trajectory if you adopt the G7 model, opposed to that G1 BC. That’s more likely to be the discrepancy than the DA miss. But like I mention, any of these three calculators will have you within 1-2clicks if your inputs are all good.
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Old 10-11-2021, 10:24 AM
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Thanks for all the info. Appreciate it. I'm guessing there are a few other variables that come into play too such as barrel length even bullet neck tension which can play into things at longer distances (granted 700 yards isn't long compared to what some of you shoot). I am going to use the data I printed out as a starting point then jot down any adjustments my rifle/load need and create my own specific dope sheet. I won't be doing much traveling with this rifle and my elevations will almost always be between 1300-2200 ft which wouldn't be a drastic change at my ranges. At least I don't think so.
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Old 10-11-2021, 01:12 PM
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If you know your station pressure (bar pressure where you are at) altitude is a moot point!
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