Velocity node

[CLB1973]

Who looks for the optimal charge weight by looking for a velocity node via the chrono? I'm curious, do you feel like this helps fine tune your load development? Reason I ask, for something to be statistically significant it requires a minimum of 30 samples. So, do you fire 30 rounds of individual charge weight and or do you shoot multiple 5 shot strings with each group a different charge weight? I'm not sure 30 is enough.

Thoughts?

 

[rijndael]

for something to be statistically significant it requires a minimum of 30 samples.

That's why I don't believe the velocity 'flat spot' exists, at least as it exists when most people 'find it', with 1-3 shots. It's also the same reason why I ignore the ES/SD posts when the Magneto shows <= 5 shots. People brag that it was 'so easy to tune' ... and that's offered as their proof.

 

[Mulligan]

CW

 

[WildBill3/75]

I do.

I use a large piece of cardboard and 300m minimum distance instead of a chronograph though and mark shots. I got a magneto speed but don't like fixing things to my barrel for this part of the process... And to lazy to get an offset mount.

You will see a band where loads shoot similar. I grab the center charge and try to develop that load and play with seating depth.

It's not rocket science. The OCW just gives you the largest band where charges shoot similarly. This makes up for some temperature deviations and/or if you don't have a super accurate powder thrower.

We are looking for consistency and the largest band where consistency is achieved.

 

[NorCalMikie]

5 or 10 rounds, all going in the same hole? You're done!
Who cares how fast the bullet gets to the target. Dead is dead. (even if it's paper)

 

[ARK]

The question is " Does the velocity node correspond to accuracy node"? Unfortunately, my flat velocity nodes rarely correspond to best groups.

 

[Jager]

I'm not sure 30 is enough, either. I feel better shooting 50-shot groups.

Only problem is that a charge weight ladder is 300 shots. Takes all afternoon.

And then a seating depth ladder has even more steps, because I'm only changing three-thousandths at a time. That takes 600 shots. Sometimes takes two days.

Actually, the biggest problem I have is once I get my rifle dialed in, the accuracy starts to go south!






Sorry. Just kidding!

No, love my Labradar and use it all the time, but chrono flat spots are little more than a curiosity for me. Count me in the camp that looks to the target to reveal all.

 

[Beiruty]

Most shooter think that accuracy is just a number X number of shots in a circle of Radius R.
The matter of fact R is only the mean of the dispersion, R-3SD, R+3SD is where all shots will land.

For example, a rifle is claimed to be 0.8 MOA accurate.
R= 0.4MOA
If SD=0.1 MOA (that is very consistent groups)
Then, all shots would fall in Min R= 0.1 MOA and Max R=0.7MOA That is min group size of 0.2MOA and max of 1.4 MOA. All those shots would be statistically possible from this same rifle.

 

[WildBill3/75]

5 or 10 rounds, all going in the same hole? You're done!
Who cares how fast the bullet gets to the target. Dead is dead. (even if it's paper)

Over the years I've found that most of those killer looking small groups found when only picking based on accuracy while charge weight testing shoot like crap with small changes in temperature and deviations in powder throws.

Your charges have to be dead nuts every time and you will have to develop new loads with changes of the weather.

If you get into the goldilocks zone from the start, you don't need to play with load development all the time.

The worst I generally have to do is chase the lands if accuracy starts to drop off. My charge weights generally are the same for the life of the barrel.

Everyone has their own method. I like to shoot more than develop loads.

OCW generally takes up to 25 rounds if you know the charge weights to start in. Seating depth even less.

 

[Doom]

Here we go again!

 

[DLT]

The question is " Does the velocity node correspond to accuracy node"? Unfortunately, my flat velocity nodes rarely correspond to best groups.

Same with me.

 

[STS]

So here's a question I've never seen answered. What is the origin of, or what causes the flat spots in velocity in spite of increasing powder charges? I can certainly understand a ladder test on a target at 500 yards and its ability to show where the bullets are exiting along the whip of the barrel. That test works quite well if conducted correctly. But I've never understood the logic of why a flat spot in velocity occurs, much less what it means where it really counts which is on the target.

 

[chkunz]

So here's a question I've never seen answered. What is the origin of, or what causes the flat spots in velocity in spite of increasing powder charges? I can certainly understand a ladder test on a target at 500 yards and its ability to show where the bullets are exiting along the whip of the barrel. That test works quite well if conducted correctly. But I've never understood the logic of why a flat spot in velocity occurs, much less what it means where it really counts which is on the target.

I have asked the same question. I have wondered if they are really flat spots, are they repeatable? What if you shot ten identical later tests and overlaid them, do the flat spots repeat? What if you shot a group of ten shots at each step in the ladder, would the flat spots just be within the variability of the hits and not really flat spots at all? I have not seen anyone shoot enough shots and collect enough data to answer these questions. Maybe it has been done and the data recorded and presented for all to see and I have just missed it.

If this has not already been done and documented, it would be a fun experiment to do. This is something I would enjoy doing. Unfortunately, my eyesight is deteriorating and I am having difficulty shooting small groups from the bench.

 

[rijndael]

I have not seen anyone shoot enough shots and collect enough data to answer these questions.

The majority of ladder tests I see performed use 1 shot per charge, occasionally it's 3.

Imagine a load with an ES of 30. I could easily have a charge of 34.4 shootingat or below the velocity of 34.2 with loads that have that high of an ES and an insignificant sample size. That's not a flat spot, it's bad loads and sample sizes that are far too small.

 

[WildBill3/75]

If OCW was bullshit, people wouldn't do it.....
I started loading this way over 10 years ago and it made me a believer.... Before I ever picked up a chronograph.

http://www.ocwreloading.com/about.html

Tiny hole groups don't mean shit if it isn't consistent.

For the guy that asked is the data repeatable?
Yes. I've shot the exact same ladder twice and had similar results.

At the end of the day, do what works for you but don't discount something because you know nothing about it.

 

[chkunz]

Imagine a load with an ES of 30. I could easily have a charge of 34.4 shootingat or below the velocity of 34.2 with loads that have that high of an ES and an insignificant sample size. That's not a flat spot, it's bad loads and sample sizes that are far too small.

That is my point, Insufficient data can easily lead to incorrect conclusions.