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.

did you shoot it yet to see if your trajectory matches your chart?

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!

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.

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

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.

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.

If you know your station pressure (bar pressure where you are at) altitude is a moot point!

If it makes you feel any better, Bronc, 22LR drops that same 18.5moa at only 200 yards! It also passes that 135” gross drop at only 300 yards. So that 6.5 creed’s not doing too bad out there at 700yrds.

But I also want to reiterate - your physical altitude really doesn’t matter much. My private range is at 1300ft, the private club I member with is also at 1300ft, as are two of the other ranges which host PRS matches here in KS - all within 100ft physical elevation... However, at these ranges, the atmospheric conditions over the last 4-5yrs has yielded Density Altitude equivalencies from -500 up to 4800 ft. During the same single day match, between first shot fired at 8am and last fired at 3pm, I occasionally see 1000 to even 2500 ft density altitude change. So shooting and hunting 1300-2000 feet, you might have HUGE atmospheric changes which, like my own life around 1300ft, might swing your DA by thousands of feet.

Revisiting this one today - I recently had a conversation about the difference between MOA and MRAD with another shooter and it reminded me of this thread - when we look at trajectory compensation in inches, or even IPHY or MOA, the numbers get pretty big pretty fast, and the pattern can be a bit more difficult to remember... And that reminded me a bit of the "that can't be right"

For example - for my 6 Dasher, I can count on my fingers as a guide for my rough trajectory for every 100yrds, close enough to be within 2 clicks, from 300 out to 1200: I just recall that 300 is 1mil, then I start counting 400yrds at my left thumb at 1.5, then add a mil and 100yrds for every finger until I get to my right thumb, which is 900yrds, where I have to add an extra half mil, then 1mil to 1000, 1.5 for 2 fingers, and 2 for my last finger, gets me all the way to 1300yrds.

300 = 1.0
400 = 1.5 left Thumb (add 1 mil per 100yrds)
500 = 2.5 left index
600 = 3.5 left middle
700 = 4.5 left ring
800 = 5.5 left pinky
900 = 7.0 right thumb (added an extra half)
1000 = 8.0 right index (just 1mil here)
1100 = 9.5 right middle (1.5 per 100 now)
1200 = 11.0 right ring
1300 = 13.0 right pinky (2mils)

I won't be wrong by more than 2-3 clicks on any of these distances:

Estimated vs. Actual
400 = 1.5 ~ 1.7
500 = 2.5 ~ 2.6
600 = 3.5 = 3.5
700 = 4.5 = 4.5
800 = 5.5 ~ 5.6
900 = 7.0 ~ 6.8
1000 = 8.0 ~ 8.2
1100 = 9.5 ~ 9.6
1200 = 11.0 ~ 11.3
1300 = 13.0 ~ 13.1

But what's maybe more relevant for this particular thread - 13mils seems like a relatively small and manageable number, and 11 vs. 13 doesn't seem to be terribly extreme It seems a little more surprising when we consider this compensation difference in MOA - as that 2mil gap becomes ~7moa. However, if we think about that difference in linear offset instead of subtensions, that difference is actually 10 1/2 feet of difference between 1200 and 1300 yards, and the total drop compensation at 1300yrds is 51ft 2in... It's a heck of a lot easier to remember 13mils at 1300yrds than 614 inches!

Revisiting this thread AGAIN - I shot a Pro Series PRS match last weekend here in Kansas, during which we saw gusts up over 40mph, some gusts up over 50. My highest wind hold for the day was 6.1 mils at 1040yrds, shooting in a prevailing 28mph wind at my 2:30 - which is 19 feet of WIND drift. Every 2mph wind bracket was halfway across the plate, and most of our 30sec wind captures were seeing 10-12mph variability in wind speed. It was brutal.

I shot this weekend with my new "big gun," and was explaining to another shooter behind the line the actual significance of what we were doing - looking through the spotting scope, we tend to lose perspective on just far apart are our line of sight and our bullet trajectory when we are shooting long, long distances.

I had an opportunity to shoot 2913yrds this weekend, and for my first round impact on the target, I sent 35.5 mils of correction (I dialed 30.5mils on my scope, since my capacity was only 32.5), then held 5 mils in the reticle. Thinking of 5 mils in the optic, that really didn't feel like too much - not so different than when I HOLD OVER from my 100yrd zero when shooting at ~750yrds, since both would be a 5mil hold in the reticle... but recalling the 30.5mils extra dialed, PLUS the 5 mils held, totaling 35.5, I had to acknowledge that I was actually aiming my bore more than100yrds (310ft 3in, to be exact), higher than the 48" target (1.6moa at 2913yrds).

Not very often in my life have I had opportunity to need to hold 100yrds ABOVE target to guide bullets where I wanted them to go. It's a really intense experience.

what. chambering?

It's a 375 Cheytac, I'm sending 400grn Cutting Edge Lazers out at 3050fps. I live an hour from one of the most pre-eminent ELR competition ranges in the country, so I don't have much excuse for not having a rifle to go play.

good answer!:)