velocity validation.

Doric

Well-Known Member
gents can I ask your take on chrono , ballistic app accuracy.
I was checking my 222 rem load out to 300 yards and found a discrepancy in both velocity and actual bullet drop from the information given with quickload and Strelock. My F1 showed a 3420 fps average with 40 grain Vmax, quickload indicates 3360 for the given powder charge, and when the indicated POI is compared to the strelock POI at 300 yards we find a 1 MOA drop difference.
I have of course set my wrap with the drops proved on paper for 1, 2, and 300 yards and intend adjusting the velocity settings on Strelock to get the drops to come in line with the proven drops which should give more accurate 10 yard increments. right?
I look forward to hearing of your thoughts.
 

dodgyknees

Well-Known Member
Follow this procedure:

Validation

Quickload output will 99% of the time be wrong. Chronographs will be wrong some of the time, varying from mostly to rarely, depending on model and meteorological conditions, and the user knowing how to set it up correctly.

The only validation that translates to accurate drop charts is a thorough drop test. Any errors in velocity and BC are corrected. It is important to do at least two tests well downrange from your zero. It is vital that altitude, pressure and temperature are input correctly into Strelok on the day. And equally important not to shoot with or into the wind. Ideally a still day.

The velocity validation is then written into Quickload with the powder burn rate adjustment. All subsequent loads with this same powder lot will be a lot closer to reality, the more validations you do, the better it gets.

The only real use for a chronograph is measuring ES, to check the load development, and to get a ballpark velocity. The high end chrono’s are pretty good, but the el cheapo ones can be a bit hit and miss. A drop test fixes this.
 
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Daddy The Skunk

Well-Known Member
I have seen chrono error verified by another unit mine was a Pact unit and had show some odd reading's when it worked at all. My Oehler Model 35 always works.
Unless you have another unit on hand to double check results what you see is what you have in terms of velocity. Drop is velocity and bc related and several things mess with real world bc so IMO the drop test is a great tool it wont be the end all to confirm velocity.
 

Daddy The Skunk

Well-Known Member
I don't bother. Yes it is simplistic and I don't shoot beyond 600 yds. No apps used no weather data to compute, a range card developed for the caliber at hand is the only reference used. Target's the size of white tail or mule deer , elk or American pronghorn have a large heart lung area . At the range I consider max on un wounded game my methods work fine. Should I be out thinning the prarie dog population I keep my shots under 600 yds unless I get the itch to stretch things. the P dogs are the size of a pint bottle . As to what I do consider, wind velocity, wind value, mirage. Temps encountered dictate powder choice for thermal stability.
 

dodgyknees

Well-Known Member
Well in that case the drop test appears to be the most practical way to iron out BC variances and trajectory validation, doesn't it!
 

jcampbellsmith

Well-Known Member
gents can I ask your take on chrono , ballistic app accuracy.....
The only thing that I would add, is to document your visits to the range. Validation is an incremental process. As you better understand your kit, the results will improve. I like Strelok Pro and it's worthwhile looking at the options it gives for truing up your results. Like everything else we do, practice will improve the outcome. Writing up after a visit to the range also helps you to review what you did and why you did it.
Regards
JCS
 

borbal

Member
I am not quite sure what you mean by "BC variances". Do you mean variations of BC for the same bullets out of the same box? Or do you mean variance of BC from what is stated on the box - or bullet manufacturer's data?

I think it is pretty well known now that the G1 ballistic coefficients that are often quoted for bullets - worked up as they were from blunt cannon projectiles - are not suitable for the pointed "Spitzer" bullets most people shoot. But most bullet manufacturers are now sensitive to this and either quote G1 BCs appropriate for different velocity ranges, and/or a more a appropriate G7 ballistic coefficient.

There are any number of online calculators (including my own) that will compute accurate drop tables for the particular shape of bullet that you intend to use. With that, you can create a drop table for use in the field.

Your biggest problem, though, is estimating the range of your quarry in the field - not how accurate your drop table is. No matter how good your drop table is, if you can't estimate the range correctly, you are not going to hit what you are aiming at. That will take a lot of practice - which will do you no harm at all. Or, you can shell out a not inconsiderable amount of cash and get a laser rangefinder, which a lot of stalkers these days think is an indispensable piece of kit....

GK
 

dodgyknees

Well-Known Member
I am not quite sure what you mean by "BC variances". Do you mean variations of BC for the same bullets out of the same box? Or do you mean variance of BC from what is stated on the box - or bullet manufacturer's data?
All of the above. On a few occasions now, we've had bullets from one lot to another, purportedly the same, that are in fact slightly different... different ogive forms for example.

There are any number of online calculators (including my own) that will compute accurate drop tables for the particular shape of bullet that you intend to use. With that, you can create a drop table for use in the field.
But if you don't have an accurate velocity to start with, you start with bad data. This is something we have proven by testing different chronographs side by side, in different conditions. Not everyone has a Lab Radar! A two or three range drop test / trajectory validation irons out the errors in velocity and BC (if any). Do it properly, use a good app, and then test on a small (e.g. half MOA) gong at our typical open country hunting ranges, and you're away. This is the normal, established method for the medium and long range shooters here, drop testing loads that are accurate to within a specified limit at the zero range. The logic is the same for me culling deer at 500m and those choosing to shoot tahr at 1000m.

Or, you can shell out a not inconsiderable amount of cash and get a laser rangefinder, which a lot of stalkers these days think is an indispensable piece of kit....
It is... for us. We all have them, various brands, we've tested them side by side as well. The thought of not having one wouldn't even enter my head. Indispensable is indeed the correct word. Angle compensated (horizontal distance) capability is a given. When the damn thing stops working (e.g. flat battery) it is good to know how to use the reticle for ranging, though depending on calibre and cartridge, after a certain point it starts to get way too imprecise. That is why I carry three rangefinder batteries.
 
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Outback

Well-Known Member
What Dodgyknees said ! with the crono result and your drop targets you alter the BC value on Strelock on the velocity / BC validater section . not the velocity . it gives you the choice on the two .
 

Doric

Well-Known Member
Gentlemen, thank you for taking the time to respond to my query most of which backs up my thoughts. Thanks outback for pointing me towards altering the bc value rather than velocity. I will let you know my findings when the wind drops which is not often in north east Scotland.
 

dodgyknees

Well-Known Member
What Dodgyknees said ! with the crono result and your drop targets you alter the BC value on Strelock on the velocity / BC validater section . not the velocity . it gives you the choice on the two .
Hmmm. I would caution against this. If you read up on this and spend time with the proper long range guys, you’ll learn that they very rarely alter a modern factory proven G7 value.

I suggest taking a long hard look at some of the amended BC values required to match drop tested velocity to what the chrono says. If you do this enough you realise that you are having to change the BC to an unrealistic value in relation to the factory published value. In my experience, when you start to stretch your shooting out to longer ranges you will find fiddling with the BC means you’ll run into problems. Whereas leaving the BC static and altering velocity results in more consistent outcomes.

At the end of the day there is no substitute for a high-quality chronograph that you trust. This is the part that your own independent testing must resolve - is the reported MV real? This is where I’ve seen with my own eyes too many variances between chronographs. My own consistent experience with chronographs has been a slight under reading of muzzle velocity which results in me shooting high in the field. So at 600m, I’ll clean miss a goat when aiming at the high shoulder. A quick drop test always resolves this.

Of all the chronographs we’ve played with, the MagnetoSpeed seemed to be the most reliable. That said, one of our best known custom long range hunting rifle makers always drop tests his loads before he hands the rifle over to the client. He will tell you that there is always a variance between the MagnetoSpeed reading and the drop tested result, and that the post drop test validated trajectory is the one that is handed over to the client. And he never fiddles with BC.

There are some really cool articles out there that discussed this in detail. Some are pro-drop test, others are pro-expensive chronographs. But few recommend fiddling with G7 BCs of the current crop of extensively tested efficient bullets.

I think that Igor made a mistake including the BC field in the trajectory validation on Strelok! If you read the instructions for truing by ballistic coefficient, he uses an example of having to alter BC from 0.447 to 0.407. That is completely unrealistic! If you do some mock ups of assumed muzzle velocity versus a drop test outcome you will see how much you have to alter the G1 value to get it to work. We have fiddled with this function in the field with high quality chronographs and good drop test data, and the amount we have had to alter BC to get it to match is just not right. Ask the bullet manufacturers like Hornady if that amount of variance is realistic and they will simply tell you no, we have full confidence in our Doppler radar data. At which point you really do need to ask yourself if you know better than they do.

In all honesty, the biggest contributor to differences on the day is the weather!
 
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Sonicdmb73

Well-Known Member
gents can I ask your take on chrono , ballistic app accuracy.
I was checking my 222 rem load out to 300 yards and found a discrepancy in both velocity and actual bullet drop from the information given with quickload and Strelock. My F1 showed a 3420 fps average with 40 grain Vmax, quickload indicates 3360 for the given powder charge, and when the indicated POI is compared to the strelock POI at 300 yards we find a 1 MOA drop difference.
I have of course set my wrap with the drops proved on paper for 1, 2, and 300 yards and intend adjusting the velocity settings on Strelock to get the drops to come in line with the proven drops which should give more accurate 10 yard increments. right?
I look forward to hearing of your thoughts.
One thing I will mention is that Strelok and most other ballistic apps assume that you have used the second “zero” ie when the bullet is travelling down from the line of sight. 61228964-3D4A-4ECA-93C6-CE0BBE2244B6.jpeg
Otherwise you are not going to get accurate data. Try zeroing your 222 at 150 yards or better still 200. Then check drop to 300plus and see what you get.
A friend went on a long range day with Richard Utting, he was told to get the StrelokPro app. Then they zeroed and trued the data. I don’t believe that either BC or speed were changed just the zero distance.
I bought one of the rifles he took, it is accurate out to 600 yards which is about the limit for the cartridge.
 

dodgyknees

Well-Known Member
It’s also worth mentioning that truing BC is the domain of the proper very long range guys. I guess I should specify that what I do is only tested out to 700m or so, as I don’t shoot further than that as there’s no need. Just had an interesting Whatsapp chat with the one mate who says “true velocity out to 600m then consider BC adjustments based on drop data at 1200m”.

Well I won’t be doing that. But he’s adamant that velocity is the key component of drop out to say 600m and that if you try and adjust BC to match actual drops at that range, you’ll stuff the ballistics completely. Which is what we discovered trying to do it this way at 500m. So we are aligned on that.
 

borbal

Member
In my experience, when you start to stretch your shooting out to longer ranges you will find fiddling with the BC means you’ll run into problems. Whereas leaving the BC static and altering velocity results in more consistent outcomes.
What is the point of measuring muzzle velocity then? You might as well leave the chrony at home and just work off measured drops at given ranges...

GK
 

borbal

Member
Measuring muzzle velocity gets you in the ball park.
Regards
JCS
We seem to be just done agreeing that "ballpark" is not good enough. The only thing that is good enough is measuring drops at known distances. In fact, the upshot would seem to be that a stalker is best putting the cash (s)he would have spent on a chronograph towards a laser rangefinder, as that is a far more necessary piece of kit. The reason is that the BC printed on the box of bullets is not to be trusted. In fact, the whole concept of a BC is problematic.

However, there are a couple of websites which calculate the drag from the bullet shape, and then use that to compute a ballistics table directly, rather than refer to the measured ballistics of a standard projectile. All you need to do is carefully measure the required dimensions of your particular bullet, (or some manufacturers publish the dimensions of their bullets), and you should be able to produce accurate drop tables with a known muzzle velocity.

One online calculator is at JBM - Calculations - Modified Point Mass Trajectory

And the other is at Bullet Design form

GK
 

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