Why use a chronograph if I’m going to true anyway?

[Little_Fish]

I’m still learning my way through getting my inputs squared away knowing how each factor affects the others.

Aside from load development and getting data on a load’s SD, what ultimate purpose does a chronograph serve if I always true the MV in my kestrel to reality?

For example, I went to the range this weekend. I’m shooting factory loads, 6.5CM shooting a 140 ELD-M. My chrono gives an average of 2710 fps and my kestrel gave the solution of 8.55 MILs at 960 yards. However reality called for needing only ~8.4 MILs so the kestrel MV calculator changed the MV to 2747.

Why bother to use the chrono if my MV calculator is just going to override that number anyway? I’m using a BC of .296. I see a lot of talk of tweaking the BC vs the MV but I’ve never felt smart enough to do that. Using the calculated MV I was consistently getting hits out to 1000 yards so in the end I suppose everything was lined up, but I just don’t like it when numbers don’t match.

 

[KnowNothing256]

I’m still learning my way through getting my inputs squared away knowing how each factor affects the others.

Aside from load development and getting data on a load’s SD, what ultimate purpose does a chronograph serve if I always true the MV in my kestrel to reality?

For example, I went to the range this weekend. I’m shooting factory loads, 6.5CM shooting a 140 ELD-M. My chrono gives an average of 2710 fps and my kestrel gave the solution of 8.55 MILs at 960 yards. However reality called for needing only ~8.4 MILs so the kestrel MV calculator changed the MV to 2747.

Why bother to use the chrono if my MV calculator is just going to override that number anyway? I’m using a BC of .296. I see a lot of talk of tweaking the BC vs the MV but I’ve never felt smart enough to do that. Using the calculated MV I was consistently getting hits out to 1000 yards so in the end I suppose everything was lined up, but I just don’t like it when numbers don’t match.

Fundamentally I agree with your premise. You don't need a MV if you have the ability to verify trajectory out to your farthest desired target distance.

In practice, I'd use a somewhat different method than you are. I'd true MV somewhere around 500-600 yds on paper or a very small steel plate (1 MOA or less); if you can't hold that small a group, then you should use paper and shoot more rounds. Either way, minor BC errors have negligible effect at those ranges, but do come into play out past 800 or so. So, true MV at 5-600, then BC at 1000 or so; the Applied Ballistics folks recommend truing BC at transsonic distances which can be even further, but some people run out of range distance before they can get transsonic.

 

[Little_Fish]

Fundamentally I agree with your premise. You don't need a MV if you have the ability to verify trajectory out to your farthest desired target distance.

In practice, I'd use a somewhat different method than you are. I'd true MV somewhere around 500-600 yds on paper or a very small steel plate (1 MOA or less); if you can't hold that small a group, then you should use paper and shoot more rounds. Either way, minor BC errors have negligible effect at those ranges, but do come into play out past 800 or so. So, true MV at 5-600, then BC at 1000 or so; the Applied Ballistics folks recommend truing BC at transsonic distances which can be even further, but some people run out of range distance before they can get transsonic.

Thanks, I’ve heard that method before. The range I shoot at ends at 1,000 yards so I cant get transonic.

I did just go back and check my chrono data. While using the average, I was not thinking about the ES, which was high at a 47 fps spread (factory ammo remember). So at the high and low end of that range the difference is 0.4 MILs. So yes while the average is one thing, without more consistent ammo, I can’t ever possibly predict how every single bullet will fly, I can only center my dispersion and hope for the best. Thinking about it in terms of that makes things make more sense. I only used 3-4 shots at distance to true the MV, and that is most certainly not enough to reliably get good enough data to make the most informed choice.

Which I suppose brings me full circle as to why the chrono is important.

 

[Ledzep]

If your zero, optics, and drag/dynamic models are decent, then you should be able to use accurate MV information and achieve accurate results.

If you have to lie about MV to get things to line up, it's a good indication the drag model is inaccurate or your optics/zero are not accurate.

YMMV.

 

[kthomas]

If your zero, optics, and drag/dynamic models are decent, then you should be able to use accurate MV information and achieve accurate results.

If you have to lie about MV to get things to line up, it's a good indication the drag model is inaccurate or your optics/zero are not accurate.

YMMV.

I tend to agree with this.

I've never had to tweak my ballistics software to get accurate results if the inputs are correct. No issues with using an MV straight from a chrono.

I suspect something is amiss with your inputs on your ballistics solver.

 

[Little_Fish]

I tend to agree with this.

I've never had to tweak my ballistics software to get accurate results if the inputs are correct. No issues with using an MV straight from a chrono.

I suspect something is amiss with your inputs on your ballistics solver.

What inputs would be the most to check? BC? Otherwise it’s height above bore and bullet info.

 

[kthomas]

What inputs would be the most to check? BC? Otherwise it’s height above bore and bullet info.

The issue with using BC is that its one measurement taken at a static point in time. BC's of projectiles will change as velocity changes throughout the flight of that projectile. Short distances this isn't an issue, but longer distances this reality comes into play.

If you use applied ballistics, I find their custom drag models to be very precise. They account for the above, through doppler measurements recorded with specific projectiles. If you don't have access to those, and you use a kestrel, you can do the DSF (drop scale factor) to help calibrate BC. I believe there's some YouTube videos that can help you through using the DSF function if you're not familiar with it.

Other than that - yeah, basic inputs like height above bore should be at least close. Make sure to use real time environmental conditions, as things like DA can swing wildly throughout a day of shooting. Using consistent projectiles (such as Bergers), help as well. And using ammo that has consistent MV (i.e. low SD's) helps as well. If you have an Sd of 20+, then there's only so much your ballistic calculator can do if the bullet that just left the barrel is 70 fps off from the MV input.

 

[ma smith]

Chrono for load dev mostly.

You can definitely do long-range shooting without it....provided you have time, good range access, quality notebook, a good spotter...and plenty of ammo, etc.

But the chrono gives you operational flexibility, and acts as a process check on guesses/or assumptions when deciphering actual-dope as well.

you can't really tease all the detailed info out with dope since you just get the one number, whereas the chrono lets you control for MV, so you can solve parallel equations in mulitiple variables a bit easier...

if that makes sense...its useful. if not, you also might just prefer a simpler process with more shooting/reptitions to get your data that way.

 

[Taylorbok]

If everything is squared away I can use the number off my chronograph and get impacts out to 2400 yards. (using an AB custom drag model)
So basically I don't true MV

 

[Supersubes]

I’m still learning my way through getting my inputs squared away knowing how each factor affects the others.

Aside from load development and getting data on a load’s SD, what ultimate purpose does a chronograph serve if I always true the MV in my kestrel to reality?

For example, I went to the range this weekend. I’m shooting factory loads, 6.5CM shooting a 140 ELD-M. My chrono gives an average of 2710 fps and my kestrel gave the solution of 8.55 MILs at 960 yards. However reality called for needing only ~8.4 MILs so the kestrel MV calculator changed the MV to 2747.

Why bother to use the chrono if my MV calculator is just going to override that number anyway? I’m using a BC of .296. I see a lot of talk of tweaking the BC vs the MV but I’ve never felt smart enough to do that. Using the calculated MV I was consistently getting hits out to 1000 yards so in the end I suppose everything was lined up, but I just don’t like it when numbers don’t match.

Seems like you may have a scope tracking issue. Ive never had to fudge a 140 eld bc down that far. I use the mach 2 BC of .320 and the number off my chrono, and its remarkably close across many different custom barrels.

 

[Taylorbok]

Seems like you may have a scope tracking issue. Ive never had to fudge a 140 eld bc down that far. I use the mach 2 BC of .320 and the number off my chrono, and its remarkably close across many different custom barrels.

it's mind numbing the amount of potential error there is in the system all to be +/- .1 mil. That being said I agree fudging the BC down that much should not be necessary.

 

[Ledzep]

What inputs would be the most to check? BC? Otherwise it’s height above bore and bullet info.

Scope over bore at the objective lens, zero (range or angle) of 10+ rounds, parallax free as precise as possible. All environmental data input to match current reality. A scope tracking test never hurts.

4DoF uses Cd vs. Mach data gathered with doppler radar over the entire Mach regime of flight and has some other built-in physics that handle aerodynamic jump and wind drift very accurately. The AB solver with the CDM's is also reasonably accurate although with some more limitations (mostly wind/AJ related) but should be no problem to get a 6.5 with 140's hitting out to 800+yd regardless.

If you're using a single-input BC solver... You're going to get errors with many projectiles. The BC value (G1 or G7) is fluctuating through the Mach regime so a single input value is cutting corners and will be high/low in various areas.

Anyway, lying to the program about MV is going to shift the Cd vs. Mach values the program references and usually causes bigger issues than changing BC, especially when you change temperature, altitude, locations, etc. Again, though, a single BC value is a compromised approach in 2024 IMHO.

 

[6.5SH]

What inputs would be the most to check? BC? Otherwise it’s height above bore and bullet info.

That your zero distance is correct as well as truly being zeroed. The first one is more common than you think because people assume their public or club range is 100 yards and ends up being 92 or 106 etc. Zeroing at an odd distance is fine, but that is the number that needs to be entered.

Use of an app like On-target or Ballistic-X to measure the group size and actual ATZ may reveal that your zero isn't one. If it fell in between adjustments on the scope that is what the offset function is for. Again, what is entered into any ballistic calculator needs to be accurate; garbage in, garbage out.

Sources of Ballistic Program Inaccuracies:
http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/

 

[Taylorbok]

Scope over bore at the objective lens

I've always taken HOB at the turrets.

 

[Ledzep]

The image that the erector tube "sees" is generated at the objective lens. It's usually not a huge difference .030-.050 depending on rail angle.

 

[Little_Fish]

The issue with using BC is that its one measurement taken at a static point in time. BC's of projectiles will change as velocity changes throughout the flight of that projectile. Short distances this isn't an issue, but longer distances this reality comes into play.

If you use applied ballistics, I find their custom drag models to be very precise. They account for the above, through doppler measurements recorded with specific projectiles. If you don't have access to those, and you use a kestrel, you can do the DSF (drop scale factor) to help calibrate BC. I believe there's some YouTube videos that can help you through using the DSF function if you're not familiar with it.

Other than that - yeah, basic inputs like height above bore should be at least close. Make sure to use real time environmental conditions, as things like DA can swing wildly throughout a day of shooting. Using consistent projectiles (such as Bergers), help as well. And using ammo that has consistent MV (i.e. low SD's) helps as well. If you have an Sd of 20+, then there's only so much your ballistic calculator can do if the bullet that just left the barrel is 70 fps off from the MV input.

I'm using AB in my Kestrel, but I don't have access to the custom curves since I don't have the elite model. It's on my list of things to upgrade, but I haven't done it yet. This might push me there since I've seen a lot of talk about using the custom curves vs the G1 or G7.

Seems like you may have a scope tracking issue. Ive never had to fudge a 140 eld bc down that far. I use the mach 2 BC of .320 and the number off my chrono, and its remarkably close across many different custom barrels.

I did a tall target test to check tracking a few months ago and my scope was spot on.

it's mind numbing the amount of potential error there is in the system all to be +/- .1 mil. That being said I agree fudging the BC down that much should not be necessary.

I'm not fudging BC at all right now. The number of .291 is from AB while Hornady publishes .326 I believe.

That your zero distance is correct as well as truly being zeroed. The first one is more common than you think because people assume their public or club range is 100 yards and ends up being 92 or 106 etc. Zeroing at an odd distance is fine, but that is the number that needs to be entered.

Use of an app like On-target or Ballistic-X to measure the group size and actual ATZ may reveal that your zero isn't one. If it fell in between adjustments on the scope that is what the offset function is for. Again, what is entered into any ballistic calculator needs to be accurate; garbage in, garbage out.

Sources of Ballistic Program Inaccuracies:
http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/

This is definitely something I don't do. I always always leave the ATZ as zero when in reality I know it isn't true. Hard to measure the day of the match since I can't go down range.

I've always taken HOB at the turrets.

lol SAME.

 

[Supersubes]

I'm using AB in my Kestrel, but I don't have access to the custom curves since I don't have the elite model. It's on my list of things to upgrade, but I haven't done it yet. This might push me there since I've seen a lot of talk about using the custom curves vs the G1 or G7.

I did a tall target test to check tracking a few months ago and my scope was spot on.

I'm not fudging BC at all right now. The number of .291 is from AB while Hornady publishes .326 I believe.

This is definitely something I don't do. I always always leave the ATZ as zero when in reality I know it isn't true. Hard to measure the day of the match since I can't go down range.

lol SAME.

Hornady publishes 3 BC’s in velocity bands. .326 is only going to apply for a little over 200 yds. By 600 yds its .310. You could try your inputs in Hornady 4 dof and see how they compare. Or return your velocity to 2710 and see what BC spits out 8.4.

Litz’s own Acoustic derived BC was .322 if I recall,

 

[Rio Precision Gunworks]

Like many things we use in the loading room and range, a chronograph is a diagnostic tool. You use it to find issues or confirm things working.

When you use it for ammo, you are weeding out inconsistent ammo (and thusly processes or components that contribute to inconsistency), or confirming consistent ammo.

When you use it for data/dope management, you are finding incorrect inputs in the software. Be it the user inputs, or the bullet data such as BC. If you're having to make large changes, you know something is up. Sometimes you will still have to fudge numbers, but that typically means the BC or bullet info is incorrect (assuming the user inputs are correct), and you can work with the manufacturer of the bullet or software to figure out why. Or you are using it to confirm your inputs and such are correct.


The TLDR: the chronograph is used the same for everything we do. Troubleshooting or confirming. Can you do a lot or most without it? Yes. Will it take longer without the chronic than with? Also yes.

 

[45-90]

There are no absolute values, but the gustimate on the chronograph is useful as it gives the velocity data needed, to show your S/D good or bad, to begin to see if the bullet powder choice will be acceptable.

I don't correct the velocity, I correct the BC of the bullet....but they both change depending on conditions.
Do the corrections at 650 yds with your lazer rangefinder. Always use your chronograph and electronic gagets, used by you.
So 308 Win case, 200 gr SMK 2856 ave fps, L A, chassis, Bartlein 8 twist 7.32 U ML wind 1.41/ 1.58 L 7:30 10 mph target 088° 1000 yds. G7 .360
Kestrel was on at 1000yds, that day. But I don't use it much, and I chronograph most everything to get an idea of how my ammo is preforming.
No one cares, so do what works for you, chronograph or No.
Mostly I just use a rangefinder, notes, and dial up the range, watch for impact and adjust, old school...or load a tracer in the 50BMG, that works too.

 

[Little_Fish]

Hornady publishes 3 BC’s in velocity bands. .326 is only going to apply for a little over 200 yds. By 600 yds its .310. You could try your inputs in Hornady 4 dof and see how they compare. Or return your velocity to 2710 and see what BC spits out 8.4.

Litz’s own Acoustic derived BC was .322 if I recall,

A BC of .309 gives me the 8.4 at 2710 compared to the .296 I was using.

 

[Little_Fish]

Hornady publishes 3 BC’s in velocity bands. .326 is only going to apply for a little over 200 yds. By 600 yds its .310. You could try your inputs in Hornady 4 dof and see how they compare. Or return your velocity to 2710 and see what BC spits out 8.4.

Litz’s own Acoustic derived BC was .322 if I recall,

Oh and in 4DOF all environmentals and inputs the same, the solution is 8.41. So it would seem that the BC I was using from AB is flawed, at least for my situation.

 

[bulletbluesky]

I’m still learning my way through getting my inputs squared away knowing how each factor affects the others.

Aside from load development and getting data on a load’s SD, what ultimate purpose does a chronograph serve if I always true the MV in my kestrel to reality?

For example, I went to the range this weekend. I’m shooting factory loads, 6.5CM shooting a 140 ELD-M. My chrono gives an average of 2710 fps and my kestrel gave the solution of 8.55 MILs at 960 yards. However reality called for needing only ~8.4 MILs so the kestrel MV calculator changed the MV to 2747.

Why bother to use the chrono if my MV calculator is just going to override that number anyway? I’m using a BC of .296. I see a lot of talk of tweaking the BC vs the MV but I’ve never felt smart enough to do that. Using the calculated MV I was consistently getting hits out to 1000 yards so in the end I suppose everything was lined up, but I just don’t like it when numbers don’t match.

It's always good to know what's the consistency of your ammo from your rifle. And how it changes vs ambient temperature etc. As of average BC consistency I agree with you. Cd curve itself is a subject of change from shot to shot (depends on the quality of ammo, enviromental factors etc). For 6.5 CM and factory ammo, radar data is going to give something like this:

Without radar you have to chronograph it at least at two places downrange to get an idea of the consistency

 

[308pirate]

I’m still learning my way through getting my inputs squared away knowing how each factor affects the others.

Aside from load development and getting data on a load’s SD, what ultimate purpose does a chronograph serve if I always true the MV in my kestrel to reality?

For example, I went to the range this weekend. I’m shooting factory loads, 6.5CM shooting a 140 ELD-M. My chrono gives an average of 2710 fps and my kestrel gave the solution of 8.55 MILs at 960 yards. However reality called for needing only ~8.4 MILs so the kestrel MV calculator changed the MV to 2747.

Why bother to use the chrono if my MV calculator is just going to override that number anyway? I’m using a BC of .296. I see a lot of talk of tweaking the BC vs the MV but I’ve never felt smart enough to do that. Using the calculated MV I was consistently getting hits out to 1000 yards so in the end I suppose everything was lined up, but I just don’t like it when numbers don’t match.

Do you really think that muzzle velocity varies so much every time you go shoot?

Figure out what your average muzzle velocity is with a chronograph, then make sure your drag curves, rifle setup, and environmental inputs are correct.

The whole point of this is to make a first round hit. What you're doing is a first round miss then "truing" to get a hit.

 

[Little_Fish]

Do you really think that muzzle velocity varies so much every time you go shoot?

Figure out what your average muzzle velocity is with a chronograph, then make sure your drag curves, rifle setup, and environmental inputs are correct.

The whole point of this is to make a first round hit. What you're doing is a first round miss then "truing" to get a hit.

Yes, I shoot factory ammo so I’ve found the MV varies between lots enough that I need to check it at least once per each lot.

 

[308pirate]

Yes, I shoot factory ammo so I’ve found the MV varies between lots enough that I need to check it at least once per each lot.

Do you realize that you just answered your own question why you need a chronograph?

I dare you to learn how to shoot without an app on your phone.

 

[Taylorbok]

The image that the erector tube "sees" is generated at the objective lens. It's usually not a huge difference .030-.050 depending on rail angle.

Makes sense, I'll start measuring at objective, every bit counts.

I'm not fudging BC at all right now. The number of .291 is from AB while Hornady publishes .326 I believe.

Litz’s own Acoustic derived BC was .322 if I recall,

A BC of .309 gives me the 8.4 at 2710 compared to the .296 I was using.

These are some pretty darn big swings. Hornady publishes .326, AB library shows .296, If all the other info in your calculator is spot on (including using a measured MV) and .309 makes it line up that's the BC I would use.

 

[ma smith]

If you don't want to true the inputs, there's always a more expensive kestrel !

 

[Taylorbok]

If you don't want to true the inputs, there's always a more expensive kestrel !

For free you could download 4DoF on your phone and see how the results compare.

 

[DocUSMCRetired]

Important uses for a chronograph:

1) To check SD, ES, and Consistency of the load.
2) To log and evaluate different powders temperature sensitivity.
3) To make sure rimfire ammo is not transonic clipping when you don't want it to.

And other reasons as well....

 

[Supersubes]

Important uses for a chronograph:

1) To check SD, ES, and Consistency of the load.
2) To log and evaluate different powders temperature sensitivity.
3) To make sure rimfire ammo is not transonic clipping when you don't want it to.

And other reasons as well....

Doc, whats the deal with the AB .291 G7 for the 140 eld? Seems oddly low. It disagrees with Litz’s earlier acoustic chrono numbers, which matched well with Hornady’s current doppler numbers.

 

[45-90]

Bullet BC is not a constant value...it changes, with every influence, and velocity, from bullet to bullet,...no two bullets have exactly the same profile, weight & length variations exist...plus your barrel twist rate can make a big difference.

 

[Supersubes]

Bullet BC is not a constant value...it changes, with every influence, and velocity, from bullet to bullet,...no two bullets have exactly the same profile, weight & length variations exist...plus your barrel twist rate can make a big difference.

Me and others have already said this very same thing in this thread multiple times.

AB has likely fired the 140 ELD out of many barrels/twists at many different velocities, for years and years. Why would their BC be at the extreme low end? Seems odd, that's all.

 

[Little_Fish]

Doc, whats the deal with the AB .291 G7 for the 140 eld? Seems oddly low. It disagrees with Litz’s earlier acoustic chrono numbers, which matched well with Hornady’s current doppler numbers.

Yeah that’s a good question for @DocUSMCRetired. It used to be .291 and now it’s .296 which is all still really low.

 

[ma smith]

Yeah that’s a good question for @DocUSMCRetired. It used to be .291 and now it’s .296 which is all still really low.

Ya'll are spoiled LOL...go look at some 6mm bullets before you call .296 G7 a low BC...

J/K

 

[diggler1833]

I've found my cheap chronograph usually requires me to add 20-30 FPS when I true velocity at 600 - 650 yards. However, I trust the ES and SD. When it says that they are tight, I see it downrange too. I use calipers to get as accurate a scope height as possible. And I know my elevation and keep track of atmospheric conditions.

I didn't use a chronograph on the last rifle of my buddy's. Shot a couple back-to-back groups that were everything I could want at 100. Guessed at the velocity based off of Hodgdon's load data. Shot a confirmation group that was just as tight at 385 yards, but ended up a tenth high. Recalculated for an additional 55 FPS using a ballistic calculator. Shot it at 650 and was dead nuts on. Vertical was 1.25", so I'm going to assume that the ES and SD are pretty tight too. Shot one final group at 650 again a few days later with duplicated results. Plugged that data in, and smoked a crow at 244 on my next Shot, followed by a coyote at 258 the shot after. At this point, there is an extremely small velocity window that gives me the correct drop at 250, 385, and 650...so I'm confident in the velocity too.

I'm a big fan of the chronograph. Not only for ES and SD, but also when trying to obtain a velocity goal while staying within observable pressure limits. Do I use one all the time? Maybe 90% of the time, but I'm also blessed with being able to shoot off my porch or out of my shop...and don't have to drive to a range. I'd use a chronograph 100% of the time if it meant I wasn't wasting gas money and windshield time.

 

[DocUSMCRetired]

Doc, whats the deal with the AB .291 G7 for the 140 eld? Seems oddly low. It disagrees with Litz’s earlier acoustic chrono numbers, which matched well with Hornady’s current doppler numbers.

We purchase our bullets through online distributors and not from Hornady directly. This is the performance we measured of the ones we received. If you check the PDMs. You will find the BC for those bullets across dozens of rifles ranges from 0.281 to 0.310. Looking at the actual data they have a variance of more than 12% between different lots. This is across multiple dozens of PDMs we have generated. They do tend to hover around the 0.292 area for the most part lately.

That is one of the beauties of building a PDM database. You can see the variance in different manufacturers bullets.

 

[Taylorbok]

I've found my cheap chronograph usually requires me to add 20-30 FPS when I true velocity at 600 - 650 yards.

If it’s an optical you need to add for the distance away from the muzzle you placed the chrony because they don’t extrapolate back the actual MV. I can’t remember the exact number but IIRC it’s roughly 1fps per foot.

 

[diggler1833]

If it’s an optical you need to add for the distance away from the muzzle you placed the chrony because they don’t extrapolate back the actual MV. I can’t remember the exact number but IIRC it’s roughly 1fps per foot.

Very true.

I am absolutely using an initial velocity for my calculations that is (very) slightly reduced over a true velocity. In my case, I'm about 9' away.

 

[DocUSMCRetired]

If it’s an optical you need to add for the distance away from the muzzle you placed the chrony because they don’t extrapolate back the actual MV. I can’t remember the exact number but IIRC it’s roughly 1fps per foot.

Here you go: https://appliedballisticsllc.com/wp...city-Decay-between-Muzzle-and-Chronograph.pdf

 

[Chanonry2]

Chrono for load dev mostly.

Yes. I have always struggled with the Labrador and now Garmin devices. Neat, handy yes. But $$$ for something that really I will only use occasionally.

Why shoot with it all the time?