Magnetospeed vs Calculated MV

[Bigwheels]

Help me out here. I'm trying to understand why my ballistics apps, & programs are ALWAYS requiring a higher MV than my chrony's are giving. I've been wrestling with this since FFS DeltaIII (which I'm still using) going back over 2 barrels on my 300WM.
This last time out I was testing the 225 ELDM vs the 230 Hyb @ 1400+, and 1700+ yds. Now given where I live all my long range shooting must be done in the mountains so I realize that I'm sometimes contending with up/dn drafts but this time I detected no measurable wind @ the time of firing and there was no apparent mirage. Perfect conditions. I was shooting downhill by -6* from 2000'asl to 1500'asl where the TGT was on a small low ridge in the middle of the big valley. All my ballistics said I needed about 1 moa higher than actual. 43.5+/- a click while actual was 42.25 moa.
I just re-read the article on mirage by the South Texas Shooting Sports, and I'm wondering if it could have been a temp inversion I was shooting through in the early morning causing a Superior Mirage causing my impacts to be High, but surely that would have gone away as the day wore on and I moved to the 1700+ yd TGT when the sun was fully out, and the wind picked up causing horrible mirage that could be easily seen. Also as I said earlier I have been wrestling with this conundrum for years. I can't be shooting through Superior Mirage all the time.
So, what are your opinions on the accuracy of the Magnetospeed? Is it accurate enough to trust it over the Calculated MV obtained by FFS, AB, 4DOF, TRASOL, & Streloc? since ALL but Streloc corrected the MV to 2865+/- a bit to bring the DOPE inline with actual observations. For some reason Streloc corrected to 2840ish. No idea why that one was so low, while AB corrected it to 2870ish. The Magnetospeed said my Average was 2820fps.
Input from the pro's appreciated.
Thanks.

 

[Jefe's Dope]

tag

 

[morganlamprecht]

how is your mid range dope? if i was checking velocity id be shooting things in the 400-800 yds range

id be adjusting BC out past 800...i havent spent much time past 1500, but the times ive shot 1400-1500, the magneto speed + adjusted BC (from 800-1100) had me on targets with the calculators ive used

im sure a few guys who've spent more time at 1500+ will chime in shortly

 

[Steel+Killer]

Tag......

 

[Bigwheels]

I did a preliminary MV calibration @ 910yd. Still needed a little higher to get on @ 1400.

 

[Lonestar1027]

This probably won't help, but I'm having a similar issue with a 6.5 Creed. Magnetospeed showing 2825fps, Kestrel with AB showing I am up near 2865fps based on dope at 400, 550, and 1k yards. Interested to see if anyone has a solution for you.

 

[Alan101]

I’m in the same boat. Mine never match. Remember that BC is velocity dependent so if you are running your load hard your BC in the program may not be correct. Try putting your crono velocity in program and adjust BC in the program to make your program match real world DOPE. This works for me.

 

[Bigwheels]

I would like to get some ideas myself. Like I said. I've been questioning the chrony'd velocity vs calculated for over 3000 rnds 2 barrels & 3 chronys. I even stacked 2 shooting chronys one behind the other & only used the results that agreed between the two & still had to increase the MV in my software to jive with observations.
It must be something simple...

 

[Bigwheels]

I've tried that more times than I can remember. Either way it's off one way or the other. Now I'm using bullets 'Doppler verified' BC's with custom drag curves & drag coefficients.
I might try going to a place I know where I can set up over flat ground & see what happens. But that spot is 200 miles away.

 

[Apnea]

Tagged

 

[BJames]

Tag

 

[Tony1320]

What scope are you using? Have you done a tall target test to confirm your scope tracks true?

Have you trued your BC?

 

[_Windrider_]

You need to true your BC before your velocity. @morganlamprecht was leading you down tha path.

 

[Bigwheels]

Scope is a NXS 5-22x56 & I have measured my scope calibration 3 times for verification.
I discussed the subject with Blaine Fields of FFS a long time ago & he told me that I should adjust MV 1st at mid range & then do the final round by adjusting the BC &/or DK at the verge of transonic.
Now back then nobody used Doppler BC & Magnetospeed chronographs so maybe things have changed but that still seems counterintuitive that the BC would be wrong by that much. Especially needing it to increase above published numbers.

 

[Bigwheels]

So I just did a quick check & with TRASOL & my measured MV to get my observed DOPE for 1400yds the BC would need to increase to about .815 G1. This NC also works @ 900yds but is too high for my observed DOPE for 1700.
I spent several hours last night playing with all my ballistics software & most required 2865 fps with DK & BC adjustments to get as close as possible to the observed DOPE for the 3 ranges I've tested.

 

[Tony1320]

Are you using G1 BC in your Ballistic Calculators?

If so try it with G7 BC

 

[Bigwheels]

Some software like FFS only use a G1 & the others that accept a G7 I have used it. Frankly either will work & ones like FFS Trasol & 4DOF only use the BC to convert it to a Drag Curve.
I have always managed to get accurate results but I question why the measured numbers don't get it done. If the manufacturer has 'Doppler Verified BC' & the Magnetospeed is that accurate why don't the numbers add up?
It can't be anything like shooting position since those variables will be baked into the guns zero.

 

[Tony1320]

Manufacturer BC's are never accurate. Bryan Litz has a book with accurate BC of bullets but for your application I would be using a custom drag model.

Have you tried Applied Ballistics using the custom drag model?

 

[Diver160651]

You need to true your BC before your velocity. @morganlamprecht was leading you down tha path.

This is misleading at best. Yes, I know this came out of AB. But it is most-likely taken or used a bit out of context.

All the solvers will have the same issue, if your short range velocity is not fixed first.

If the short range drops does not line using paper, measuring any offset (be it .25” or whatever) at 300 thru 500 ish you have a velocity (or range) issue. This must be addressed FIRST. Too many people skip this part and it will come back an bit you in the butt "if" you care about hitting a tiny 300y target and a really far target with the same dope. The rub is a lot of people never step this stuff out and it goes un-noticed.. Some might have rock solid dope to 1K.. some at 600-1600 others at 1500 - 2500, but none of that means that the curve is working as expected across all the distances. This is true for all solvers..

Here is a real example that I have seen for years..The distances must be exact, your zero perfect or the offset accounted for.

Let’s say at 400y your perfectly chrono’d round with a .618BC going 3100fps hit .5” high at 400yards. At 1750 is was low 5MOA...

AB, CB,JBM and FFS all will have the same outcome..

Please show me how adjusting the the BC, FIRST can balance this curve..

I have shown example of this over and over.. but maybe it make more impact if those not believing it run thru the it themselves. Use JBM or whatever, see how much you need to whack your BC make this work.. Then look at what happens to your velocity..

 

[Tony1320]

@Lowlight can you chime in?

 

[morganlamprecht]

This is misleading at best. Yes, I know this came out of AB. But it is most likely taken a bit out of context.

If the drops does not line using paper an measuring any offset (be it .25” or whatever) at 300 thru 500 ish you have a velocity issue. This must be addressed FIRST.

The distances must be exact, your zero perfect or the offset accounted for.

Here is a real example that I have seen for years..

Let’s say at 400y your perfectly chrono’d round with a .618BC going 3100fps hit .5” high at 400yards. At 1750 is was low 3 minutes...

Please show me how adjusting the the BC, FIRST can balance this curve..

im thinkin what dillhole was trying to say since he referenced my post was...you need to true your BC first, at the distances the OP is talking about (900+ yds), not velocity...velocity should be handled well before you get out to 1400+ yds...maybe just a miscomm

 

[Bigwheels]

Divers post almost exactly mirrors what Blaine Fields of FFS told me years ago.
Basically the BC of the bullet does not begin to affect trajectory until it has been in flight for a time therefore MV must be addressed 1st at mid range. Also mid range is cartridge dependant. Midrange for a 308 is shorter than midrange for a 300WM.
I'm using AB with custom drag curves & the ballistics correction page adjusts MV in the 1st bracket. Then the second bracket adjusts the drag curves.
I understand the process well enough. I'm just curious why with all the new technology we can't simply put in the numbers & roll on?

 

[Tony1320]

Does your mid range dope line up?

This is really interesting I'd love to know more

 

[Bigwheels]

I adjusted the MV to line up @ 900yds. I needed to increase it about 30-40fps. Don't have my notes in front of me.
Then @ 1400 it was low again but @ 1700 I hit high. Magnetospeed said my average is 2820fps but most of my software wants 2865-2872fps to be close. Then I adjusted the BC & drag curves.
I'm very confident of my DOPE @ 900 & 1400 but it was later in the day when I moved out to 1700 & the mirage there was terrible with switching wind so less confident of my DOPE. But when I read the mirage right I hit.
My buddy has a magnetospeed also & I might swap him for a few shots to see if there's a change.

 

[Diver160651]

Divers post almost exactly mirrors what Blaine Fields of FFS told me years ago.
Basically the BC of the bullet does not begin to affect trajectory until it has been in flight for a time therefore MV must be addressed 1st at mid range. Also mid range is cartridge dependant. Midrange for a 308 is shorter than midrange for a 300WM.
I'm using AB with custom drag curves & the ballistics correction page adjusts MV in the 1st bracket. Then the second bracket adjusts the drag curves.
I understand the process well enough. I'm just curious why with all the new technology we can't simply put in the numbers & roll on?

Ya, I wasn't saying you don't.. But some of the feedback on here obviously didn't. I was not even really addressing your issues, sorry..

In your specific example, you have no way on confirming whats actually going on.. did the position you build have you drive the gun slightly differently (lighter dive can cause higher impacts) .. is the MV off just a hair.. is the range finder perfect etc.. I mean a tiny 1% ranging error at 1700 make more than a minute of difference in perfect conditions. A switching 270/90 10mph wind is a minute.. Mirage will generally have you aim high..

If your within 1 min at that distance your distance with off angle shooting etc.. I think that's really good, your second shoot should be money

Now if your high, then low, then high.. it is almost always a slight range error

 

[Tony1320]

How far off was the elevation at 900 yards?

I wonder if the difference is because I believe Nightforce click values are .26 not .25 at 1700 yards that might account for your difference?

But you said you confirmed tall target test what was the result?

Have you confirmed distance? How are you determining distance?

 

[Bigwheels]

Absolutely correct. I used my Sig 2400 with reflectors on the tgt stand & backed that up with my Bushnell lrf. They both gave the same read +/- a tenth on the Kilo. I'll get another buddy to come along with his Terapin as well. Position was prone every time. Doing everything in my power to be as accurate as possible.
I can easily understand the variables past 1000 but inside that my gear should be accurate & my MV always needs to be increased to match.

 

[Bigwheels]

As for my scope calibration I put the scope in a vice at the shop & measured 50yds with a 300' tape made a moa scale with my calipers & ran it through 50moa & back several times. Results were 1.015/click which gives .2538 moa/click.
I may do it again with live fire as well when the weather cooperates.

 

[_Windrider_]

im thinkin what dillhole was trying to say since he referenced my post was...you need to true your BC first, at the distances the OP is talking about (900+ yds), not velocity...velocity should be handled well before you get out to 1400+ yds...maybe just a miscomm

If I know my velocity is good because I have a Labrador next me on every shot the only variable is BC. Obviously there is a point where u can over true your BC and there is a point where both need to be tweaked but I’ve never had to adjust my MV by more than 20-25 FPS after getting a real BC based on my MV, not what’s published on the box (which is only valid at 59f 29.92 and 0% RH at their measured MV).

 

[Tony1320]

I would do a live fire verification

If your clicks are .2538 vs .261 could that be where the difference is ?

43.5 divide by .261 = 166.6
43.5 divide by .2538 = 171.3

 

[Bigwheels]

I just might do that along with a revarification of zero again.
If you haven't noticed I'm a little anal about things. I've been a mechanic for 30 yrs & to me all this is like an engine that isn't running quite right. A problem needs solving.

 

[_Windrider_]

I adjusted the MV to line up @ 900yds. I needed to increase it about 30-40fps. Don't have my notes in front of me.
Then @ 1400 it was low again but @ 1700 I hit high. Magnetospeed said my average is 2820fps but most of my software wants 2865-2872fps to be close. Then I adjusted the BC & drag curves.
I'm very confident of my DOPE @ 900 & 1400 but it was later in the day when I moved out to 1700 & the mirage there was terrible with switching wind so less confident of my DOPE. But when I read the mirage right I hit.
My buddy has a magnetospeed also & I might swap him for a few shots to see if there's a change.

You aren’t verifying dope with MS on your rifle are you? That will definitely skew it. Get your MV, take the MS off then gather dope. Otherwise you could have errors in there when shooting with no MS.

 

[Bigwheels]

My Magnetospeed is free floated & I have verified it does not change my poi when it's on. So yes I am checking my velocities while I'm shooting.

 

[_Windrider_]

My Magnetospeed is free floated & I have verified it does not change my poi when it's on. So yes I am checking my velocities while I'm shooting.

Roger that.

 

[Snuby642]

G1 or g7?
At 1/3 the ranges your shooting my bc changes impact data.
Im thinking farther you go the more it will show.
So shine me on I'm not undertanding about the choice of using g1 on a bullet that looks and preforms like a g7?
Wont that throw off the bc, maybe especially going transonic?

I had reverse trouble with subs, accidentally going sonic and the bc dope went out the window by more than 1 moa at short range.
So a high speed low drag g7 bullet being fed g1 dope?

Spent an hour and a half last nite transfering dope to a designated rang phone be cause it would not choke down the generated file.

 

[Bigwheels]

Most of the software I'm using doesn't actually calculate the solution using the BC. They take the BC & basically convert it to a coefficient of drag so G1 vs G7 is really irrelevant.

 

[Bigwheels]

Yes that is the case when it's clamped on the barrel. However in a previous post I said that mine is not. Mine is mounted on a picitini rail free floated in position with no part of it touching the barrel.

 

[Bigwheels]

Checked my zero again which I came up 1 click & did a live fire tall tgt test. After measuring the tall target through 50 moa it was different from my previous measurements by .005. I measured the scope in a vice at the shop at a measured 50yds on a target I marked every 5 moa with my calipers & came up with a correction factor of 1.015. The live fire came up with 1.010. However I will continue to use my original numbers. The tall target has a bit of mirage & potential group center variables. So I'm still in the same place only I did get some shooting in.

 

[Deleted member 113831]

What twist on that barrel? If you are using a 9 twist or faster then you could be seeing a BC increase.

Also, we shoot in the same valley. I can tell you that the angle of the sun has a fairly dramatic effect the way it comes up and bounces light through that valley. Shooting on one of our many overcast light neutral days is the only way to eliminate that variable.

 

[Tony1320]

Checked my zero again which I came up 1 click & did a live fire tall tgt test. After measuring the tall target through 50 moa it was different from my previous measurements by .005. I measured the scope in a vice at the shop at a measured 50yds on a target I marked every 5 moa with my calipers & came up with a correction factor of 1.015. The live fire came up with 1.010. However I will continue to use my original numbers. The tall target has a bit of mirage & potential group center variables. So I'm still in the same place only I did get some shooting in.

That's solid tracking. I believe within 1% is acceptable

I'm out of ideas I hope you are able to figure it out.

Post some pictures of where you shoot 1700 yards if you don't mind... I'm pretty jealous lol

 

[Bigwheels]

Yeah I'm pretty confident in my original scope calibration. So I'm discounting that as the issue. The new barrel is a 9.5 twist & even on the lower end of my measured velocity my stability runs @ 1.5 but I have to assume that they got the BC right with the right twist during testing. The 1 click I adjusted in my zero actually made it worse so I had to redo all my settings again to flatten the drops even more.
So now my MV has to be 2872 to get close on most of the apps. FFS needed to be 2880. After going through all this again I have to think that the Magnetospeed is just reading low.
I don't think the light effected my DOPE at 900 & 1400 since it was overcast & almost no wind in the early morning. Also I shot the 1400 yd tgt twice with the same results.
Pouring rain & 20 mph wind this weekend with no end in sight right now. I'll find a pic of one of my spots for you later.
I'll update when I get a chance to shoot again.
Thanks for the help.

 

[Bigwheels]

This is my favorite spot. Snowed in right now. I can set up targets almost anywhere from point blank to 2400 yds. It's behind a locked gate that I have access to.

 

[Jefe's Dope]

OMG! You lucky bass turd.

 

[Diver160651]

Out West we have A LOT of open space, but the overall gun cultural is threatened (mainly in our 3 Weatern coastal states) It is not all a free lunch.

 

[Tony1320]

View attachment 6891501
This is my favorite spot. Snowed in right now. I can set up targets almost anywhere from point blank to 2400 yds. It's behind a locked gate that I have access to.

That is a beautiful view. You are a lucky man

I'll be right over lol

 

[Tony1320]

Yeah I'm pretty confident in my original scope calibration. So I'm discounting that as the issue. The new barrel is a 9.5 twist & even on the lower end of my measured velocity my stability runs @ 1.5 but I have to assume that they got the BC right with the right twist during testing. The 1 click I adjusted in my zero actually made it worse so I had to redo all my settings again to flatten the drops even more.
So now my MV has to be 2872 to get close on most of the apps. FFS needed to be 2880. After going through all this again I have to think that the Magnetospeed is just reading low.
I don't think the light effected my DOPE at 900 & 1400 since it was overcast & almost no wind in the early morning. Also I shot the 1400 yd tgt twice with the same results.
Pouring rain & 20 mph wind this weekend with no end in sight right now. I'll find a pic of one of my spots for you later.
I'll update when I get a chance to shoot again.
Thanks for the help.

Any chance you have access to a Labradar to confirm?

Sounds good thanks!

 

[Bigwheels]

Don't know anyone with a Labradar but next time out i will probably bting my old Shooting Chrony & also swap my buddies Magnetospeed to get more data to work with.
Another thing is that my previous 10 twist barrel was running the 230gr Berger @ 2900fps with about the same charge so I think it's entirely possible that my MV is much closer to that than the 2820fps my Magnetospeed is telling me.

 

[Diver160651]

Any chance you have access to a Labradar to confirm?

Sounds good thanks!

Because he is striving for perfection, as mentioned he needs to account for true MV that the solver expects, not another chronograph's reading.

The very best thing he can do is get on a windless, mirage-less mid morning day in a location were he can shoot his 100 zero and a 500y/m, 900 and trans target at the same time, same AOF both on paper and confirm that he has zero offsets.

This is anal stuff, if the load ES to large this becomes only academic anyway.

Using the example of the solver rifle data I posted earlier, a 8fps offset in any chronograph shout show up as about .25" at 500 yards.. We need to understand that's almost nothing and goes un-noticed. That's only a .0026 error in the chrono. To get the same movement in BC at 500 yards you need to make an adjustment that is about 9.23x the % of the MV adjustment.

So what makes sense to adjust? BTW the same is true for a 1" off elevation strike on a plate.. That still a tiny chrono offset of about .0104 so, we call it center and move on, but that is not how to confirm your MV if your really trying to get to the bottom of an issue.

Now, just about 1 arms length error in range will make about the same .25" POI shift..

I hope for those following worrying about the twist of his barrel etc.. get that it is all nonsense to chase first.

After all the mechanical stuff, the day's shooter offset, including, super small 100 yard groups and low ES/SD and environmental conditions eliminated as much as possible, to tune, Range, range range confirmation, MV drop (short Range), BC for these calibers about 900ish.. and then first part of trans etc.. Unfortunately needs to be done under the same time/day for best results.

 

[Bigwheels]

Agreed. However I have little opportunity to shoot both short & long range from the same FFP. My best chance will be when I can get back to the place I posted the pic. The lay of the land just doesn't allow for it. But I press on feebly with what I have.
Really it doesn't matter what inputs are in there as long as I get accurate results. On the other hand I strive for everything to be correct.

 

[Deleted member 113831]

What was your actual drop at the different ranges? I ran your solution in AB and got 910 yds...21.25moa...1400 yds...42.0moa...1700 yds...59.0moa...is this close to what you saw? I used .374 G7 BC as provided in the AB bullet library and 2820fps. Average alt 1750 asl (27.7 hg) absolute pressure. Look angle -6 degrees. Scope height 1.8 inches.