What does it mean when there is no velocity/pressure node?

[MoneyWaster]

In an email to a member here from another thread I posted, I asked him about the following ladder test and results.

" How would you interpret the following data from a ladder test consisting of 7 shots per round:"

Powder – Varget Bullet – Hornady Match HPBT 75 gn.

Charge Vavg SD

23.3 2815 8.8
23.5 2847 11.8 (Best Group)
23.7 2864 10.8
23.9 2883 8.1
24.1 2892 6.4 (2nd best group)
24.3 2912 8.0
24.5 2935 8.0
24.7 2953 10.8

"What is interesting is that there is no flat spot in the charge vs. velocity graph where velocity remains constant over a range of charge values. There is a fairly linear increase in velocity with every 0.2 gn. Increase in charge weight. Does that mean that there is no node for this powder/bullet combination and I should look elsewhere?"


"If I stayed with this powder/bullet combination, would I be better served by choosing the charge weight that has the lowest SD and just assume it was poor shooting on my part that didn’t correlate the best group with the lowest SD? That SD of 6.4 at 24.1 gn. and 2893 fps looks appealing. That was actually the second best group."

What says the broader community?

 

[MoneyWaster]

In an email to a member here from another thread I posted, I asked him about the following ladder test and results.

" How would you interpret the following data from a ladder test consisting of 7 shots per round:"

Powder – Varget Bullet – Hornady Match HPBT 75 gn.

Charge Vavg SD

23.3 2815 8.8
23.5 2847 11.8 (Best Group)
23.7 2864 10.8
23.9 2883 8.1
24.1 2892 6.4 (2nd best group)
24.3 2912 8.0
24.5 2935 8.0
24.7 2953 10.8

"What is interesting is that there is no flat spot in the charge vs. velocity graph where velocity remains constant over a range of charge values. There is a fairly linear increase in velocity with every 0.2 gn. Increase in charge weight. Does that mean that there is no node for this powder/bullet combination and I should look elsewhere?"


"If I stayed with this powder/bullet combination, would I be better served by choosing the charge weight that has the lowest SD and just assume it was poor shooting on my part that didn’t correlate the best group with the lowest SD? That SD of 6.4 at 24.1 gn. and 2893 fps looks appealing. That was actually the second best group."

What says the broader community?

This is out of a 26" Bartlein M24 8 twist barrel.

 

[MoneyWaster]

This is out of a 26" Bartlein M24 8 twist barrel.

Sorry, .223 Remington bolt gun. Trued Remington 700 SS action in an XLR Carbon chassis.

 

[dkhunt14]

I shoot ladders farther out then 100. I like a minimum or 300. I use the same aiming point and 2 or 3 shots per load. I look where more then one load shoots to the same spot. I color the bullets with sharpie so I can tell them apart. I also go about .3 per load. When I find the flat spot I will load up 5 and see how it groups. Matt

 

[ireload2]

I think it is a bit erroneous to assume there will always be a flat spot.

 

[CharlieNC]

I assume you are looking for one because you have read it exists. But what is the physical reason this should be so, I don't know of one? I've also seen where guys have done this with one shot per charge, thus ignoring the fact that the ES/SD which exists at each charge insures any answer is possible. So what did the target say?

 

[Jet]

Recommend you do what Matt says and push your testing distance out further. Don't pay attention to which load(s) shoot the smallest group or which has the best chronograph #s. Find the flat spot where different powder weights hold the same point of impact, pick the weight in the middle of that then start a seating depth test.

Once you find the seating depth that works go back to small powder changes (+/-) then try different neck tension.

Good shooting

Rich

 

[dkhunt14]

I think it is a bit erroneous to assume there will always be a flat spot.

At 1000 yards there is always a flat spot, where two or more charges overlap. Sometimes more then one, sometimes it's big and somtimes it's small. It is the place where the bullet exits the barrel the same. Usually has nothing to do with velocity changes. A slower load can shoot high and a faster load can shoot low. Matt

 

[billlarson]

Sd does not always = best group.......... test groups at distance they will be used at...... +300 yds....
bill

 

[MoneyWaster]

I assume you are looking for one because you have read it exists. But what is the physical reason this should be so, I don't know of one? I've also seen where guys have done this with one shot per charge, thus ignoring the fact that the ES/SD which exists at each charge insures any answer is possible. So what did the target say?

CharlieNC,

You are correct. I have read that it exists. There is even a 6.5 Guys YouTube load development video which is fundamentally based on this phenomena.

That's why I questioned my load. There is no "flat spot" in the charge vs. velocity curve.

I agree with you that from an objective standpoint the phenomena should not exist. Pressure correlates to velocity, and an increase in charge weight should result in a predictable increase in velocity assuming the same internal case volume from load to load. And yet, here we are with many online examples showing ranges of load densities in which, when graphed, there is a flat spot in the charge vs. velocity curve where the increase in charge weight did not yield a predictable or consistent increase in velocity; a "flat spot". I have no explanation for this.

The target told me with a 0.55" 7 shot group at 100 yards that the 23.5 gn charge yielding 2847 fps was the best load.

 

[CharlieNC]

Money I have watched that video where they chrono one shot per charge to define the flat spot. So tell me, if any given charge has an expected ES that is greater than the velocity change at the next charge, do you have any confidence you can reproduce a curve with a flat spot? You can plot a series of perfectly random numbers and observe what you think is a flat spot, but reproduce it. You saw nothing because the average of the seven shots was much more representative of the smooth increase, vs one shot where you can convince yourself of anything. I will not say with certainty that the phenomenon does not exist, but I have not personally observed it while the target gives a clear story. And the confidence in limited chrono data is just that, limited.

 

[divingin]

I always thought you tested for a series of charges that hit the same place, not that shot at the same velocity.

 

[Webster]

In an email to a member here from another thread I posted, I asked him about the following ladder test and results.

" How would you interpret the following data from a ladder test consisting of 7 shots per round:"

Powder – Varget Bullet – Hornady Match HPBT 75 gn.

Charge Vavg SD

23.3 2815 8.8
23.5 2847 11.8 (Best Group)
23.7 2864 10.8
23.9 2883 8.1
24.1 2892 6.4 (2nd best group)
24.3 2912 8.0
24.5 2935 8.0
24.7 2953 10.8

"What is interesting is that there is no flat spot in the charge vs. velocity graph where velocity remains constant over a range of charge values. There is a fairly linear increase in velocity with every 0.2 gn. Increase in charge weight. Does that mean that there is no node for this powder/bullet combination and I should look elsewhere?"


"If I stayed with this powder/bullet combination, would I be better served by choosing the charge weight that has the lowest SD and just assume it was poor shooting on my part that didn’t correlate the best group with the lowest SD? That SD of 6.4 at 24.1 gn. and 2893 fps looks appealing. That was actually the second best group."

What says the broader community?

Small and round at the distance you will shoot at.

 

[MoneyWaster]

You saw nothing because the average of the seven shots was much more representative of the smooth increase, vs one shot where you can convince yourself of anything.

Indeed, your point here is very valid based on my understanding of statistics and process control.

 

[ireload2]

It may only be your imagination. Try shooting your flat spot 5 times at long range and see what happens. You may never get the same flat spot twice. It is the same phenomenon that gives you are tiny group now and then that you can never repeat.

At 1000 yards there is always a flat spot, where two or more charges overlap. Sometimes more then one, sometimes it's big and somtimes it's small. It is the place where the bullet exits the barrel the same. Usually has nothing to do with velocity changes. A slower load can shoot high and a faster load can shoot low. Matt

 

[dkhunt14]

It may only be your imagination. Try shooting your flat spot 5 times at long range and see what happens. You may never get the same flat spot twice. It is the same phenomenon that gives you are tiny group now and then that you can never repeat.

It does repeat. If you have guns good enough to see it. Those tiny groups turn into tiny aggregates. It is the way to find the node for long range shooting. Matt

 

[Mulligan]

It may only be your imagination. Try shooting your flat spot 5 times at long range and see what happens. You may never get the same flat spot twice. It is the same phenomenon that gives you are tiny group now and then that you can never repeat.

Kinda snarky isn't it?
CW

 

[ronemus]

"What is interesting is that there is no flat spot in the charge vs. velocity graph where velocity remains constant over a range of charge values."

You and the responders are talking at cross purposes. A ladder test looks for a range of velocities velocities where the point of impact on the target overlaps for several charge weights. The ladder does not look for a range of charges for which the velocity remains constant; this is generally not seen because adding powder increases velocity except under extreme circumstances.

 

[MoneyWaster]

"What is interesting is that there is no flat spot in the charge vs. velocity graph where velocity remains constant over a range of charge values."

You and the responders are talking at cross purposes. A ladder test looks for a range of velocities velocities where the point of impact on the target overlaps for several charge weights. The ladder does not look for a range of charges for which the velocity remains constant; this is generally not seen because adding powder increases velocity except under extreme circumstances.

I hear you, but that isn't what the 6.5 Guys video was proposing.

 

[dsculley]

If you watched/listened to the entire presentation you will note that Scott Satterlee believes his reloading system/technique is consistent enough for this method to work. Your results may vary.

I would suggest that load 3 rounds of each of your test charges and shoot an OCW. 100 ads shot round robin. Load 3 rounds to shoot as fighters/foulers. Your OCW will all be shot with a warm barrel. If you are not sure your seating depth is good you may want to test for seating depth first. After you shoot the OCW, post a picture of your target.