Load Work Up: Interpreting Chronograph Data

[Cole440]

Well folks, I loaded a bunch of 6.5 Creedmoor. I only intended to shoot two shots at each charge weight and then shoot 5 for the groups that seemed promising. But, I got so interested looking at the data that I went ahead and shot all 50 shots. I don't see any pronounced flat spots in the velocity curve like I at times have in the past. These were shot over the magnetospeed only, I did not shoot groups.

The shots that are are either omitted or included in the red-colored cells are shots that had brass that I know was different (over sized) so I am ok with throwing those numbers out since I identified them ahead of time with sharpie on the casings. The first photo has them omitted from the calculations, while the second has them included.

Based on the numbers, I am thinking that I will go out and shoot 40.8, 42, and 42.2 at paper and see what the groups say. Thoughts? I know you can only tell so much by the numbers and paper doesn't lie, but I thought I would see what some smarter folks than me think...

 

[straightshooter1]

Well folks, I loaded a bunch of 6.5 Creedmoor. I only intended to shoot two shots at each charge weight and then shoot 5 for the groups that seemed promising. But, I got so interested looking at the data that I went ahead and shot all 50 shots. I don't see any pronounced flat spots in the velocity curve like I at times have in the past. These were shot over the magnetospeed only, I did not shoot groups.

The shots that are are either omitted or included in the red-colored cells are shots that had brass that I know was different (over sized) so I am ok with throwing those numbers out since I identified them ahead of time with sharpie on the casings. The first photo has them omitted from the calculations, while the second has them included.

Based on the numbers, I am thinking that I will go out and shoot 40.8, 42, and 42.2 at paper and see what the groups say. Thoughts? I know you can only tell so much by the numbers and paper doesn't lie, but I thought I would see what some smarter folks than me think...
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View attachment 8180354

Your graph is exactly what one would expect to see when there's many more shots than one to look for a "flat spot"; the graph will be very much linear (particularly if one's loading is pretty consistent). If one shoots just one round for each load, some variations in the cartridges will produce some kind of flat spot somewhere, but not consistently in the same spot. Looking for and/or using such flat spots is a waist of time and components. What you might learn from the data (like the SD's and ES's for each charge) is how consistent you're case prep and the loading your cartridges is. Looking at ES's can give you some idea of how well a load performs, but not without how it correlates with the groups produced by those cartridges.

Shooting groups and interpreting the groups shape and position that each load produced (like OCW testing) will give you a much better read on which load you should go with. And even then, given just one such test of 3 or 5 shot groups, you'll want to verify with follow up to test and see if the load that you think is good does produce what you think it has (the loads have got to be repeatable).

 

[Cole440]

You're graph is exactly what one would expect to see when there's many more shots than one to look for a "flat spot"; the graph will be very much linear (particularly if one's loading is pretty consistent). If one shoots just one round for each load, some variations in the cartridges will produce some kind of flat spot somewhere, but not consistently in the same spot. Looking for and/or using such flat spots is a waist of time and components. What you might learn from the data (like the SD's and ES's for each charge) is how consistent you're case prep and the loading your cartridges is. Looking at ES's can give you some idea of how well a load performs, but not without how it correlates with the groups produced by those cartridges.

Shooting groups and interpreting the groups shape and position that each load produced (like OCW testing) will give you a much better read on which load you should go with. And even then, given just one such test of 3 or 5 shot groups, you'll want to verify with follow up to test and see if the load that you think is good does produce what you think it has (the loads have got to be repeatable).

All great info and along the lines of what I was thinking.

Like I said, this whole 50 shot thing was more of an experiment to gather data than anything. Any range trip is a good range trip and I just kind of wanted to see what happened!

Shooting groups in the velocity window I’m looking for is definitely where I’m going to go next.

 

[Doom]

All great info and along the lines of what I was thinking.

Like I said, this whole 50 shot thing was more of an experiment to gather data than anything. Any range trip is a good range trip and I just kind of wanted to see what happened!

Shooting groups in the velocity window I’m looking for is definitely where I’m going to go next.

Looking at your SD's I will tell you that when you evaluate the differences using standard statistical tools (F Test in this case) the only one that is statistically less than the largest, 14.3 is the 2.1/4.7 for the 42.2 charge. What the SD's do tell you on a qualitative bases is that you are producing pretty consistent ammunition.

 

[AllenOne1]

I would look hard at 40.8 - 41.0 grains. Low SD and average velocity is close.

 

[MarkyMark007]

national champion is not looking at velocity and ES/SD anymore:



so why snipers hide experts want to interpret every fps in your velocity ?

 

[AllenOne1]

national champion is not looking at velocity and ES/SD anymore:



so why snipers hide experts want to interpret every fps in your velocity ?

You may not have noticed but he didn't give us any groups to look at, so if any help was to be offered for his question "interpreting chronograph data" the only information available was velocity and SD.

In addition I always look at velocity to make sure I'm not running faster or slower than I should be for the cartridge in question. If you have experience with the cartridge you will know if you are in the right range by the velocity. The component mix demands that you check this unless you are using the same combination that you have always used including lot numbers. Even a new chamber/barrel can have a dramatic effect on velocity.

Then we can move on to shooting and reading the groups.

 

[straightshooter1]

You may not have noticed but he didn't give us any groups to look at, so if any help was to be offered for his question "interpreting chronograph data" the only information available was velocity and SD.

In addition I always look at velocity to make sure I'm not running faster or slower than I should be for the cartridge in question. If you have experience with the cartridge you will know if you are in the right range by the velocity. The component mix demands that you check this unless you are using the same combination that you have always used including lot numbers. Even a new chamber/barrel can have a dramatic effect on velocity.

Then we can move on to shooting and reading the groups.

Because OP didn't give us any groups to look at is why I mention that looking at velocity flat spots is a waist of time and components. Like the video, it's interpreting the groups size and shape (as well as location, for me) that tells me which load I should be using. It really is all about what we see on the target. And like you say, when there are changes in lots of powder or chambers/barrels, knowing velocity helps cut down the time and amount of components used to get a load back to working for the changes; even when there might be a change in brass or primers being used).

I keep track of velocities as it relates to the temperatures they're recorded at as well as the moisture content of the powder and seating depths. These things have an effect on accuracy/precision. Ignoring velocity all together leads to more testing than needs to be done and if extending barrel life is important, then tracking velocity is as well.

But, if you're just a plinker, none of this matters.

 

[kthomas]

That's because there are no flat spots or "nodes".

People only convince themselves that there is when they use small sample sizes.

 

[AllenOne1]

Because OP didn't give us any groups to look at is why I mention that looking at velocity flat spots is a waist of time and components. Like the video, it's interpreting the groups size and shape (as well as location, for me) that tells me which load I should be using. It really is all about what we see on the target. And like you say, when there are changes in lots of powder or chambers/barrels, knowing velocity helps cut down the time and amount of components used to get a load back to working for the changes; even when there might be a change in brass or primers being used).

I keep track of velocities as it relates to the temperatures they're recorded at as well as the moisture content of the powder and seating depths. These things have an effect on accuracy/precision. Ignoring velocity all together leads to more testing than needs to be done and if extending barrel life is important, then tracking velocity is as well.

But, if you're just a plinker, none of this matters.

After my last few matches I feel like a plinker. lol But it doesn't mean I want to be, I'm working even harder to compete at a higher level.

 

[AllenOne1]

That's because there are no flat spots or "nodes".

People only convince themselves that there is when they use small sample sizes.

On some barrels you can see flat spots, the problem is they don't repeat. On top quality barrels I don't see flat spots at all, the more powder you dump in the faster they go. Who would have guessed that would happen.

 

[CK1.0]

Yes, as your graph/data shows, more fuel = more velocity, always. There are no "flat spots" because science.

Use consitent components, prep/load every case the same as possible, drop every charge to the kernel, and seat every bullet to within a couple thou, and voila.

Pick a speed and then be the best ammo factory you can be. The monkey pulling the trigger is almost always the problem, guys who think some magic charge weight can undo any of that are ridiculous.

 

[Hickswr]

Congrats to the OP!!

You have debunked the physics defying flat spot (node) myth.

Well….actually you confirmed what AB and Hornady have been preaching for some time now.

 

[Cole440]

Don't mean to raise dust on this old thread, but I never said thank you to all of the posters for the help! I'm still referencing this now as I finally am preparing to iron this out the rest of the way!

What I've gathered is that the whole velocity node thing is a myth mostly. Put groups on target, find the velocity window I want with good groups and then go from there with seating depth. That's the plan at least

 

[Rio Precision Gunworks]

Don't mean to raise dust on this old thread, but I never said thank you to all of the posters for the help! I'm still referencing this now as I finally am preparing to iron this out the rest of the way!

What I've gathered is that the whole velocity node thing is a myth mostly. Put groups on target, find the velocity window I want with good groups and then go from there with seating depth. That's the plan at least

Yep. Consider what "flat spots" would actually entail.

You'd have to put more powder in a case and not get more velocity. More boom boom but not faster. Pretty hard thing to accomplish.