Find powder charge range in speed test

[thexman]

I recently start working on the load development for hornady 195ELD bullet using Varget.

It seems there are multiple flat points can be used for the ideal powder charge from the chart below.
a. 42.0-42.2
b. 42.6-42.8
c. 43.0-43.2
d. 43.4-43.8

My questions are:
1. Does the chart with multiple flat points look normal to you?
2. Should I test for each one of the load ranges above to find the lowest SD and ES?
3. If yes to question 2 above e.g. 43.0-43.2, should I do 5 shot groups for powder charge at 43.0, 43.1 and 43.2 to find out the best charge with lowest SD and ES, then work on the seating depth next for group size?

Thank you.

 

[BuildingConceptsllc]

How many test rounds at each charge did you shoot to get those numbers?

 

[PinesAndProjectiles]

Doesn’t matter. Flat spots are a myth. Pick a velocity you want and go from there.

 

[BuildingConceptsllc]

Doesn’t matter. Flat spots are a myth. Pick a velocity you want and go from there.

That's where I was going. After I was told it was not true and just a matter of not shooting enough at each charge to show it, I tried it out and found that my "flat spot" wasn't real.

 

[Newbie2020]

OP here’s a good place to start

Are Velocity Flat Spots a Myth?

Controversial topic here. Are velocity “flat spots” based on powder charge a myth?

www.snipershide.com

You’ll thank @MinnesotaMulisha for giving you back your life from chasing unicorn farts

 

[CanisLupus]

I recently start working on the load development for hornady 195ELD bullet using Varget.

It seems there are multiple flat points can be used for the ideal powder charge from the chart below.
a. 42.0-42.2
b. 42.6-42.8
c. 43.0-43.2
d. 43.4-43.8

My questions are:
1. Does the chart with multiple flat points look normal to you?
2. Should I test for each one of the load ranges above to find the lowest SD and ES?
3. If yes to question 2 above e.g. 43.0-43.2, should I do 5 shot groups for powder charge at 43.0, 43.1 and 43.2 to find out the best charge with lowest SD and ES, then work on the seating depth next for group size?

Thank you.

I agree with everyone else. The paper linked below is a good read to unpack this topic a little more. Jump to page 10 and read on.

https://storage.googleapis.com/wzukusers/user-33607572/documents/7f15a36e4a52403d9ac4e42ae6342116/The%20Tyranny%20of%20Statistics.pdf

 

[thexman]

Thank you guys.

So can I say to do the load development for any given rifle, would be something like this 2 steps below?
1. Do a incremental powder charge speed test to find out which MV at each charge and pick one from there.
2. Play around with seating depth to find the one giving the best group

Questions:
Do I still need to test a small range of powder charges within +/- 0.1gr range of that charge picked in step 1 to find one with lowest ES and SD? Or that's irrelevant?

 

[Dogtown]

A more granular approach would be:

1. Single shot incremental charges to identify velocities and pressure limits
2. 3-5 shot strings incremental charges within the velocity/pressure window you choose, looking for consistent velocity (low SD/ES)
3. 3-5 shot strings of chosen charge weight with incremental seating depth to find best group
4. Optionally test best load with different primers
5. Optionally test best load with incremental neck tension

EDIT: your difference between charge increments should relate be proportional to the overall charge capacity you're working with. For example, if you're doing .223REM and dealing with 20-24gr weights, you should probably increment in 0.2gr amounts. But if you're doing .338LM with 88-96gr weights, you should probably do 0.5gr amounts.

 

[Evintos]

Lowest ES and SD is fairly irrelevant because it's generally only applies for the environmental and bore condition at the time the measurements were taken.

If you want to do load development that is more forgiving of changing conditions (especially with temperature sensitive powders), you'd pick the load in the middle of a set of loads that exhibits little to no vertical POI shifts (positive compensation theory).

Example - (assume all group sizes 1" and exaggerated POI shifts for sake of example with same bullet seated depth)
Point of impacts with same point of aim.
39.6gr - low 0.36"
39.8gr - low 0.5"
40gr - center (minimal vertical spread)
40.2gr - center (minimal vertical spread)
40.4gr - center (minimal vertical spread)
40.6gr - 0.5" high
40.8gr, 0.25" high and 0.6" left

In this example, 40.2gr would be the best choice, regardless of the SD/ES of those loads. Then you would do a seating depth test to find the longest overall length that prints small groups. Has to do with the amount of jump relative to throat wear. The average velocity or the 40.2gr is the data you would use for your calculations.

Ex.
2.60 - 1" group
2.57 - 0.75" group
2.54 - 0.90" group
2.51 - 0.6" group
2.48 - 0.55" group
2.45 - 0.58" group
2.42 - 0.80" group

Choosing 2.50" COL is going to be the best bet that compensates for barrel throat wear. As the barrel wears the bullet jump increases, which is equivalent of seating the bullet deeper (which also increases jump).