So I'm running a 6mm Creedmoor and my magnetospeed is consistently saying I'm at 3100 fps. I trued my velocity on my Kestrel (older 4500 with AB) out to 878 yards and it gave me a MV of 3156. My drops now line up within that range so no issue there, my question is which source should I trust for my true velocity reading? I shoot PRS/NRL and want to make sure I have room from the 3200 fps max. I'll probably drop down to a lower node but I'm getting great results at 3100/3156 and hate to mess with a good thing.
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Actual Velocity Source?
- Thread starter Pvt.Donut
- Start date
You have several factors that influence your data: Atmospherics, velocity, ballistic coefficient, and user entered variables. I'm going to assume that your scope tracks true, you've measured your scope height correctly, twist rate, and you've entered all the other little things. If not, do it! Scope height is an important part of the total equation and if your scope doesn't track, it's useless.
That leaves atmospherics, MV, and BC. You're using a perfectly viable Kestrel, so of the remaining two, I prefer to adjust my BC instead of my MV. I know my MV. Like you, I'm using a MagnetoSpeed V3, so I know my MV is pretty accurate. The only thing I ever really question is my BC, so that's what I adjust to align my path. I view what they write on the box as a guide. For instance, I've used thousands of Hornady 140 BTHP and ELDMs. For my DOPE, a G7 of 0.285 for the BTHP and 0.318 for the ELDM lines up my data perfectly
That leaves atmospherics, MV, and BC. You're using a perfectly viable Kestrel, so of the remaining two, I prefer to adjust my BC instead of my MV. I know my MV. Like you, I'm using a MagnetoSpeed V3, so I know my MV is pretty accurate. The only thing I ever really question is my BC, so that's what I adjust to align my path. I view what they write on the box as a guide. For instance, I've used thousands of Hornady 140 BTHP and ELDMs. For my DOPE, a G7 of 0.285 for the BTHP and 0.318 for the ELDM lines up my data perfectly
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Mostly true MV at <=600yds and BC at >600yds
That being said, if you need to use 3156 in your kestrel AND it lines up with ALL your real world dope, use it. You’re within 2% of your measured velocity, so it’s not like you’re way off.
Pay no attention to the “but I measured it with a chrono so I KNOW what my velocity is” crowd. There are many things that could be a reason for the difference. What really matters is if all your real world data lines up.
In fact it’s a growing trend to use the chrono to check load consistentcy and not to even worry with the chrono speed for the calculator.
Zero at 100, then shoot it at 300. Input drop and let calculator tell you velocity. Then shoot at 600 to verify velocity/drop. Then take it out as far as possible for BC truing.
Also, don’t worry with the 3200 limit if your chrono is saying 3100. Worst case is you get chrono around 3200(never seen anyone checking speed, but who knows), and you’re not going to get DQ’d unless you’re ridiculously over it, which you shouldn’t be.
That being said, if you need to use 3156 in your kestrel AND it lines up with ALL your real world dope, use it. You’re within 2% of your measured velocity, so it’s not like you’re way off.
Pay no attention to the “but I measured it with a chrono so I KNOW what my velocity is” crowd. There are many things that could be a reason for the difference. What really matters is if all your real world data lines up.
In fact it’s a growing trend to use the chrono to check load consistentcy and not to even worry with the chrono speed for the calculator.
Zero at 100, then shoot it at 300. Input drop and let calculator tell you velocity. Then shoot at 600 to verify velocity/drop. Then take it out as far as possible for BC truing.
Also, don’t worry with the 3200 limit if your chrono is saying 3100. Worst case is you get chrono around 3200(never seen anyone checking speed, but who knows), and you’re not going to get DQ’d unless you’re ridiculously over it, which you shouldn’t be.
I assumed the Magneto could be a couple % off and I'm within that limit. Was mainly just curious if there was a consensus on whether trued velocity = actual velocity or if it was more of a way to make the numbers match up and I'm actually closer to the Magneto speeds. Good info, thanks.
Nothing is perfect, including our chrono and calculators. You may need to tweak one or both velocity and BC to get your data to line up. Don’t sweat it if you have to do either.
Now if you’re way off on either, that’s a sign that some of your other inputs may be wrong.
Basically you have two different measuring instruments from two different manufactures. I will say that there is a percentage of difference between the two. Which is better or most accurate in getting the numbers needed? Who really knows. I say they both do a excellent job.
Use the magnetto to measure the consistency of your ammo as already stated. Record the MV, keep it handy for another use that I will explain.
Now, create 2 profiles in your Kestrel. Use one profile that trues using the original kestrel way, using MV to calculate your data at edge of transonic. Use the other profile, with the known and measured MV from the magnetto and true your BC at distance. Name them so you can easily recognize which one you are using.
When you are at the range session for practice, use both profiles to see which one is most accurate for your application, and is repeatable with the changing enviormentals on different visits. You can true both profiles in one trueing session without wasting a bunch of ammo.
Use the magnetto to measure the consistency of your ammo as already stated. Record the MV, keep it handy for another use that I will explain.
Now, create 2 profiles in your Kestrel. Use one profile that trues using the original kestrel way, using MV to calculate your data at edge of transonic. Use the other profile, with the known and measured MV from the magnetto and true your BC at distance. Name them so you can easily recognize which one you are using.
When you are at the range session for practice, use both profiles to see which one is most accurate for your application, and is repeatable with the changing enviormentals on different visits. You can true both profiles in one trueing session without wasting a bunch of ammo.
I showed the error numbers to highlight that even a very small error margin, that all devices have translates to meaningful numbers at speed, highlight the need to calibrate MV in some fashion and BC at distance. It's all try dope that needs to be trued.
I use the chrono to base line my rifle and evaluate different factory ammo, and evaluate different lots. I will use the baseline to see when my barrel may be done or need cleaning.
I use the chrono to base line my rifle and evaluate different factory ammo, and evaluate different lots. I will use the baseline to see when my barrel may be done or need cleaning.
According to the manufacturer, my chrono is accurate to within +/- 1% .
Gravity is accurate to within +/- 0%.
Gravity is accurate to within +/- 0%.
From the experience I have had you should trust your chrono. And ofc be aware of varying ammo temps.
I think the muzzle velocity as a data point value is just as important as all the other data points along the flight path.
If you changed the 1000yd velocity data point to suddenly drop by 14fps or 2% or 0,15% or any other amount, it is basically just as weird as if done at the muzzle. It is like forcing two lines together at one point without looking at the whole thing.
You should be able to just make another profile, add the velocity of your round at 1000yds and its BC and it should be able to follow the same flightpath to 1200yds as the one from 0yd at the muzzle to the 1200yds.
If you do this but change both 0-1200 and 1000-1200 curves by 10fps up, they do not line up anymore. Thus the data points extrapolated before the 1000yd mark would then be invalid.
Eg. Editing the chrono data is just the same as if you moved your shooting position back or frontwards to edit your velocity at the very spot you measured the shooting distance to begin with.
In your case at 1250yds taking 14fps off would be pretty much the same as moving approximately 15-20 yards away from the target or taking 15-20 yards from the LRF reading.
Please let me know if I am wrong here. I feel dizzy.
I think the muzzle velocity as a data point value is just as important as all the other data points along the flight path.
If you changed the 1000yd velocity data point to suddenly drop by 14fps or 2% or 0,15% or any other amount, it is basically just as weird as if done at the muzzle. It is like forcing two lines together at one point without looking at the whole thing.
You should be able to just make another profile, add the velocity of your round at 1000yds and its BC and it should be able to follow the same flightpath to 1200yds as the one from 0yd at the muzzle to the 1200yds.
If you do this but change both 0-1200 and 1000-1200 curves by 10fps up, they do not line up anymore. Thus the data points extrapolated before the 1000yd mark would then be invalid.
Eg. Editing the chrono data is just the same as if you moved your shooting position back or frontwards to edit your velocity at the very spot you measured the shooting distance to begin with.
In your case at 1250yds taking 14fps off would be pretty much the same as moving approximately 15-20 yards away from the target or taking 15-20 yards from the LRF reading.
Please let me know if I am wrong here. I feel dizzy.
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Using Howlands spec of 1% from his device, at 3000fps that is a possible error of 60fps.
What the experts on these threads have told you is you need to true this in the real world between 400 and 600 yards before the BC becomes the dominate factor. Then you need to move out beyond 800 yards and true the BC or custom curve.
There are videos from kestrel and applied ballistics all over the web on this topic.
4DOF has a different but similar method to true "try" dope which is what chrono and box BC are.
Only if your chrono is 100%.
They formulas out there for the most part are trusted. So, we put in as much “known” factors as possible. When we haven’t had time to get real world data on impacts, the most known factors are velocity from chrono and trusted BC (applied ballistics, hornady 4dof, etc).
One you start gathering real world data, the most known variable in the equation is where the bullet consistently impacts.
Everything else takes a back seat, even chrono data. You tweak your velocity and BC accordingly (depending on range available).
If you have range available, you don’t even need a chronograph to make your calculator line up.
Also, by trusting your chronograph as an absolute, you are basically distrusting the formulas in the software.
Always trust in the instrumental velocity. It's very easy and cheap to compare MV using several chronos. Never, never use POI to establish velocity, it's a very bad idea, because you are mixing up a lot of potential error sources and you'll never be able to tell them apart. In short always distrust tweaking the MV.
So, you know more than the guys at kestrel and applied ballistics?
If this were they case, AB (or any other calculator) wouldn’t use velocity truing at all. As we would trust the instrumental velocity and not need to worry with it.
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Yes, it's called common sense and what AB or Kestrel is saying is BS. It's an old idea inherited from Exbal. What you are saying is simply wrong and biased info, not saying it's on you. On the other hand, if you distrust your instrument, first talk to the guys making them like Ken Oehler and you'll learn a lot in the process
Hahahahahahahahahahaha
“Common sense” is always the excuse for people who can’t articulate their opinions.
There’s a reason when you are inside of 600 yds you can barely move the calculator when adjusting BC, but you can easily move it with slight velocity tweaking.
You are so funny...problem is you need to learn a LOT before arguing...say no more. Sorry I cannot articulate but at least I can understand...what about you ? where are your so strong arguments? AB and Kestrel mantra? C'mon...gimme a break!
You are so funny...problem is you need to learn a LOT before arguing...say no more. Sorry I cannot articulate but at least I can understand...what about you ? where are your so strong arguments? AB and Kestrel mantra? C'mon...gimme a break!
Oehler goes into detail on the expected errors within the system. Be it mechanical or human error. Even says that chrono’s are a starting point, not an absolute (same as suggested BC).
Also, I already gave you an example you are unable to refute. Per most every calculator out there, velocity is the most important factor at closer distances to make the formulas work. If you are lucky enough for the velocity from the chrono to work that’s awesome. If not, you will need to tweak it.
Chrono, Velocity truing, and BC truing are all part of the equation.
Adding you to the block list. Keep peddling misinformation around. This is why you see less and less people posting on the hide other than random opinions claiming “common sense.”
Obviously there is instrumental error who says there is not? But, your argument is old, any calculator can do some number crunching until your MV "aligns" to your POI and you call it right? Ok... be my guest.
Tell me this. How can you tell apart shooter error at 600 yards? What about the natural group scattering? Can you tell where is the "right" POI? Have you ever calculated how much dispersion you got from the usual BC's 5% error found in every box? Can you?
No...you can't, neither I can. For the sake of information that kind of embedded error will yield over 1 MOA of error at 600 yards...just alone from BC.
And where is the argument I can refure? I'm still waiting...very patiently.
Like I wrote before...use several chronos like many people do and do your stats before anything else. What you are saying is simply non-sense.
Please don't try to lecture me on truing at ELR distances.
And remember this before indulging yourself, "common sense is the least common of the senses"
I agree with you, the more I test things the more BS and inaccuracy I find. Unless shooting benchrest equipment that shoots in the 0.1s out to 1000 there is too much error. We do the best we can with what we have but its certainly not what I would call "precise" I found shooting a tall target test useless group dispersion has way too much affect on results. Truing at 600-800m+ as you say the group size alone has more error in it than what we are trying to measure. Again the guys shooting bench rest with less than 1inch groups at 600-800 may be able to validate this stuff but "field rifles" have too much error. It may get you on 2 moa steel.....
I personally will go with what my magneto tells me I use it all the time the data it gives me is reliable. I believe there is less error in the magneto than there will be in my own group dispersion and ability to estimate bc etc at 800 to be going and changing the velocity.
I have seen the benchrest guys on accurate shooter talk about this stuff before and how unless you are shooting equipment that can shoot in the 0.1's you are really just having a rednecks hack at it I now fully agree.
Ye sir, you got it right. Moreover, super experienced shooters like David Tubb (plus many others) are measuring MV even when competing, that alone says a ton about the right way to assess MV.
Plus, applying some common sense, how come that BC and Drag are measured with Doppler, accoustic or systems like Oehler 88 and 89? How come the industry and the military is not doing POI-based MV truing? Are they idiots or what?
Wouldn't be exceedingly more simple and cheap to use POI and call AB and Kestrel to do their magic MV truing?
Well...the answer is NO. Even AB has a Doppler radar not for tracking velocity downrange...but to measure MV!
Just check the above picture, where we can see AB measuring MV with TWO radars, not just one...but some rednecks out there still eat whatever they feed them.
I do not like to say it but you have logic behind that. Most chronos are accurate only to 0.5 to 1% and that is a lot of play. If you get a faulty chrono (these can be found on this same forum) how can one know? The velocity differences can be spot on for testing SD and ES but just in wrong "number set"
But if you have a chrono, its reading should be still given as the base number and see if drop data is off.
If something is wrong equipment and inputs should be checked.
Eg. If your drop data shows too much drop. And MV is 'known". There is only so much change to be made by tweaking the BC with rational amount. So if you had to change BC by quite a lot and maybe "oddly much" you probably have a faulty chrono readings.
If my chrono has 0,5% margin error there is no reason not to move fps by at least that much. That's 0.25% plus or minus.
And just 0.1 Sg changes BC by 3% without counting other variables so on your first time at the range all your data is off by some amount.
I have read ABs articles and guides to calibration and they have mentioned MV cal should be performed only in ideal conditions because drop data is compromised too by just by light conditions. So only early in the morning etc.
I would gather STRONG dope and move BC for just minor 5% and then velocity for 0.25 or maybe 0.5%.
Afterall you will only see if it all works out at longer range by testing it.
Yes, and that’s without any human error involved in the chrono setup.
Nothing we do in ballistics is absolute as their are too many factors to consider.
When some people decide that one or more of the factors are absolute and not fluid (time and place for tweaking each), there’s a problem with that logic.
Perfect world, we wouldn’t need to adjust our velocity.
Any instrument in this world has built-in errors and there is not much we can do about. Like putting trust in the Kestrel or even GPS. To some extent we need to learn to live with that, it's what it is. Period. But it's no excuse to replace actual measurements of a physical quantity with some flawed algorithm based on POI. That's simple absurd.
To cope with instrumental error we need to do what every scientist will do...gatheroing lots of data to analyze with statistics tools, which is the only way to drwa smart insight on how our data behaves. On the other hand, today we have very reliable chronos and given their prices, if you are serious enough about your shooting, you can mount them in tandem to compare simultaenous readings. One more time, statistics will always shed light on what's going on in case you get some strange reading.
Nothing can take the place of a well calibrated instrument, to do the job.
My point exactly. No need to become super experts in instrumental error theory, just plain common sense and good equipment, to finally apply sound statistics.
LastShot -
I didn't track every post, but the fact that it is common to track every shot for ELR as it has been before the 35Ps, is different than the need to determine what a program is "expecting" in order to line up.
Other than to gather general load data, It is to know if the POI was a wind, mirage or actual velocity issue, not to line the program up.
This is key so that the shooters are not making POI corrections based on a round on the funky end of the ES.
Side note:
Programs like FFS have always suggested you double check your chronograph and even go so far create an offset for them, not because the instrument is flawed, but that the use of them can cause erratic results. I have seen the angles, weeds, particles (mist, dirt, snow) or structures mess with labradar's (dopplar) return velocities and well as I have with badly mounted Magneto speeds or angles with optical or acoustic. Places like Yuma don't suffer from possible human error or consumer equipment that might have been built on Friday, damaged or used incorrectly.
While I agree that the chrono should be trusted, I also am in the verify camp. But before we miss-trust the velocity or BC based on drop, a perfect zero offset must be determined, range absolute correct, no wind and certainly no visual impairments like mirage all with a very squared away shooter using paper. That "is" much harder than people sometimes think.
Jim
More food for thought, just from what I have scene on why sometimes, MV from chronos seems to be way off:
1. The most common reason chrono MV looks incorrect, is the error in lazing and getting a return from the back stop or trusting the range's distance without verifying. Lazying a small steel target is relatively hard without taking time to confirm the backstop vrs target or hitting something large next to the target or at the FFP.
2. Not accounting for a perfectly measured zero offset.
3. Shooter offset between zero confirmation and long range shooting:
1. The most common reason chrono MV looks incorrect, is the error in lazing and getting a return from the back stop or trusting the range's distance without verifying. Lazying a small steel target is relatively hard without taking time to confirm the backstop vrs target or hitting something large next to the target or at the FFP.
2. Not accounting for a perfectly measured zero offset.
3. Shooter offset between zero confirmation and long range shooting:
Anyone know someone, or remember getting a perfect zero then putting the gun to bed in the safe. Then maybe weeks later getting the gun out of the safe and having to check your zero, followed by an adjustment?
When I was 16-20 this happened to me all the time. Hell I still hear about guns shifting zero after being left unused for sometime.. I just don't think there are Safe Gremlins fucking with scopes.. It is shooter offsets, usually created by different recoil and trigger control or even a winter jacket.
This same thing can happen from trying to shoot groups at 100 focusing super hard on the groups then actually relaxing as one shoots further because can't really see the groups as well. The differences in how hard the gun was driven the trigger press and even how hard the rear bag was squeezed can all make a difference.
Basically you need to make sure your are not trying to tune 2 different "you's" into one drop curve or velocity.
4. Running a load on either the super slow or really fast end of the BC windows like Pvt.Donut in post 1, Then only tuning it for velocity a long distance.. That's kinda of the short coming using custom curves rather than stepped BCs. In this case at 3100 he will have a much higher effective BC than expected for lets say a bullet thats starts out at M2.5. Tuning only for MV (because on some programs modify the CC is not possible) at those 900yard distances then will yield an artificially high or low number.Cannot agree more
we need to double-check everything all the time. But chronos are the way to assess MV, despite their built-in errors, to that end, solid data collection and statistics.Diver160651
You also made a solid point about WIND. As we all know, wind do and will affect BC, like lighting conditions and still you have people to "true MV" with a POI-based solution. No way.
You also made a solid point about WIND. As we all know, wind do and will affect BC, like lighting conditions and still you have people to "true MV" with a POI-based solution. No way.
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