Dope for drift (1k)

[DocRDS]

Been honing my long range and discovered today that my zero wasn't 'off'--Damn earth is moving (as is my bullet).

Was 0.5 mils right shooting Bearing 270. Did a quick 4DOF and it said 0.3, but also had spin drift at 0.2.--suspiciously that adds up to 0.5 Do I need to add spin drift to my wind call (well there was no wind, usually I'm just like 'welp my wind call sucked'). Kestrel still in the car (being lazy).

Anyways is that a typical movement for a 6.5 Creed at 1k?

 

[6.5SH]

Obligatory response:

 

[Mike Casselton]

Been honing my long range and discovered today that my zero wasn't 'off'--Damn earth is moving (as is my bullet).

Was 0.5 mils right shooting Bearing 270. Did a quick 4DOF and it said 0.3, but also had spin drift at 0.2.--suspiciously that adds up to 0.5 Do I need to add spin drift to my wind call (well there was no wind, usually I'm just like 'welp my wind call sucked'). Kestrel still in the car (being lazy).

Anyways is that a typical movement for a 6.5 Creed at 1k?

Turn your earth based effects on and make sure your compass angle is correct.

 

[OREGUN]

Are you asking about spin drift or corriolis effect?

 

[DocRDS]

Both
Well my assumption is they are different.

My Assumptions:
Corriolis = Earth Spin (this is not really an assumption, pretty confident on this)
Spin Drift = movement due to spinning bullet

And it looks like I need to take both into account.

I was looking at the meter trying to true up what I was shooting. Earth Based Effects are on. Meters say 8.6 U 0.3L

Shot is 8.6U, 0.5L and no amount of fussing is gonna make it (the meter) say 0.5, however the ol spin drift says 0.2 (which suspiciously is the difference)--so my ask is do I need to add spin drift to my shot, or is it included in the "calculation" already

Obviously, I shoot 0.5L because thats an X--but If I had a vertical issue, I'd be playing with MV and BC to make my elevations line up. But I can't make my 'windage' line up on a day with no wind! Its more an "understanding" than an issue, because I got tons of data that says "AT 1000K SUBTRACT 0.5L FROM YOUR WIND CALL YOU IMBICILE" so I'm kinda gonna shoot 0.5L on a calm day.

 

[OREGUN]

I can almost promise you that if you shoot .5 left on a calm day next time you go out, you are likely to miss left. Yes, Coriolis is the earth moving. Shooting due west, it should have essentially no effect. .2 left is not unreasonable for Spindrift. The other .3 at 1000 yards could be rifle cant or some wind you’re not accounting for or bad technique or all the above.

 

[OREGUN]

I guess that didn’t really answer your question though. You can turn Spindrift on and off. If you have it on, it should be taking it into account in the number it gives you. So where is the original .3 coming from? Do you have the zone one wind set to zero? Are you saying the Kestrel says .3 but some other program is saying .2? And just out of curiosity, how much left wind do you have to add in before your Kestrel matches your actual required?


Long story short, .5 is too much to be spindrift and corriolis, even put together, IMHO.

 

[DocRDS]

9/10 times its me. Wanted to confirm I understand how the meters work (I've been wrong before).

 

[OREGUN]

To make sure I’m not bullshitting you, I got my kestrel out. Spindrift is on, latitude is set to 35’ N, direction of fire 0’.

1000 yards, 7.62U, .25L

change to DOF 270’
1000 yards, 7.68U, .25L

change to DOF 090’
1000, 7.51U, .25L

Add 9:00 wind at 2 mph, back to DOF 0’

1000 yards, 7.62U, .57L


so, point being, shooting east and west, you get a tiny change in vertical (theoretically the earth is climbing or falling relative to the flying bullet, if you believe that round earth bullshit) And when shooting north or south you get a tiny left or right change. You’ll note that the no-wind-windage, which is all spindrift, doesn’t change between east/west and north (or south, I checked). I assume the effect is too small for the kestrel to put it out.

What is notable, all it takes is 2 MPH OF WIND to get above .5mils of correction in the results. ARE YOU CERTAIN that there wasn’t 2 MPH of wind ANYWHERE in the course of the bullets flight that you didn’t feel at the firing line?

For what it’s worth, I leave my DOF on 0 because I don’t want any elevation changes due to coriolis…to eliminate the +/- .1 we see in the numbers above when I change from east to west. I do leave spindrift and aerodynamic jump on. At the distances and target sizes typical of PRS type comps, I don’t think it matters much. A tenth up or down is not a miss on a 24” plate at 1000. I leave the spindrift on because a tenth or two of spindrift and a tenth or two of wind might be a miss.

 

[6.5SH]

If you plug the same data into different calculators you will get slightly different results based on whatever model(s) they used and what biases they choose to (de)emphasize.

I did the same as Oregun in Genesis (ColdBore) with what I assumed was some flavor of 6.5 Creedmoor data and get +/- 0.1 mils elevation if shooting 270 or 90 degrees, 0 or 180 give no elevation change, all four directions will show a 0.1 mil Left correction needed with spin drift off but Coriolis/Eotvos enabled. Spin drift alone gives 0.2 mils with a 1/8 twist in this engine.

 

[DocRDS]

No, I got the kestrel out and was playing with it, I'm getting the same numbers.

It's was pretty dead this am so I am 90% sure it's not wind. Flags were dead, 0 breeze.

My suspicion is I'm canting. I did it a lot in class and I freaking hate my atlas as it won't lock down and the spuhr level is in a bad place, but ill be verifying and lining up things at distance. I'm also shooting a little low for my velocity+app, takes about 100 fps to line em up, i have MV and 1kV and it's tough getting em all synced up, and I don't have intermediate range access to confirm/redope

Last year i was happy to hit 1k, this year I'm working on 1st round hits (x ring, 7-9 dont count) and pushing 190 (20,shots) off a bipod prone. Slow progress is still progress

I mean if you get sighters, ok I can adjust. Trying to get that 1st shot X and build trust in my ballistic app.

I still yank shit at 100 ocassionly.

I'll stop rambling, but appreciate the sanity check

 

[TheOtherAndrew]

1 - AB, really al the 'algorithms' put more emphasis of effect of shooting direction/round earth than occurs in reality (according to some people I respect and my own observations afterward).

2 - Im thinking but not at all sure - is spin drift just another term for the Magnus Effect? I remember watching these ppl spin a ball off some damn dam and the ball falls in a curve. barely any for long ways then it really kicks in so perhaps its an ELR thing...difference is I think in magnus the spin rate is increasing whereas a bullets spin is only decreasing....? has that been confirmed - that a crosswind increases bullets spin or at least stops the decline (very minute stuff I get it, would need those high speed cams)?

 

[CHRIS RINER]

Been honing my long range and discovered today that my zero wasn't 'off'--Damn earth is moving (as is my bullet).

Was 0.5 mils right shooting Bearing 270. Did a quick 4DOF and it said 0.3, but also had spin drift at 0.2.--suspiciously that adds up to 0.5 Do I need to add spin drift to my wind call (well there was no wind, usually I'm just like 'welp my wind call sucked'). Kestrel still in the car (being lazy).

Anyways is that a typical movement for a 6.5 Creed at 1k?

sing drift + Coriolis on 6.5 at 1k should be about 8 inches to the right

 

[Conaso]

Shooting at an azimuth of 270 degrees there is no horizontal but a vertical Coriolis effect (Eötvös), . At that distance, you also have spin drift to account. If there is wind you would also have to account for vertical deflection of crosswind, i.e., Magnus effect. No, Magnus effect is not the same as spin drift.
Magnus Effect (negligible) - Typical bullet clockwise ↻ rotation – no wind or wind↞ = force↓, wind↠ = force↑.
Coriolis Effect - Horizontal deflection (less toward equator); shooting in N. Hemisphere - POI→, S. Hemisphere - POI←.
Eötvös Effect - Vertical deflection (less toward poles); shooting East - POI↑, West - POI↓.

 

[TheOtherAndrew]

how about 2000yds? POA center (elev dialed correctly); POI 1.5mil R/0.8milLow?

the solver emphasizes the effects too much on shorter range which dooms the calculation once higher yds used (really TOF is what were talking about across diff platforms).

 

[Newbie2020]

Can a guy just turn off earth-based effects and then true the mv and BC in my solver using confirmed dope from 300, 600, and 800 yds?

 

[DocRDS]

Can a guy just turn off earth-based effects and then true the mv and BC in my solver using confirmed dope from 300, 600, and 800 yds?

I do remember Frank saying he turned off Earth Based effects and honestly even at 1000 (as discussed earlier) they are pretty small.

TBH I think a lot of my problem is wind swirl at my range. Wind flags at the same distance can be flying in opposite directions..... I know I said there was zero wind, but evidence lately has shown we have a lot of swirl and wind effects at our range.

Did get a cold bore X this week..... and discovered my reloading practices need more OCD. (I wasn't measuring every charge and turns out my high "flyers" were a little speedy)

 

[Newbie2020]

What’s your 10-20 rd ES?