Powder ladder ?

[500Stroker]

Recently on a windy day a shot powder ladder for my 6BRX with SMK 107 bullets, Varget and BR-4 primers. My powder spread between loads was .2 grain all seated .020 off the lands.
The powder ranged from 30.2 to 32.5 gr every .2 gr, looking for the correct powder node for an accuracy load.
At first everything went as expected with the shots lining up vertically as bullet speed went up with more powder the shots went higher. Until I got to the middle of the powder range around 31.5 gr all of a sudden 3 shots went lower then the prior lower grain weight load ?
Is this common?
Could have the wind blowing left to right somehow blown them down ?
Has anyone seen this before ? Why ?
Thanks in advance for the comments.

 

[Terry]

What distance were you shooting?

Wind direction?

It makes a difference.

 

[500Stroker]

What distance were you shooting?

Wind direction?

It make a difference.

600 yards
Wind NW 10-12 mph blowing from the left to the right

 

[JamesnTN]

Ok from all years of testing and shooting over a chronograph I personally have seen loads working up as you have velocity level off and suddenly drop. What you see is a plateau on the charge, then you will see it fall off for the next .2-.3 grains and then spike after that to a higher velocity node. Then you will see again another plateau and again a drop in velocity and another spike in velocity. Depending on the case capacity to bore dia some of these spikes can be as little as 25-30 fps and upwards to 70-80fps. So what you saw on paper is exactly what is happening. Just be able to read your brass and bolt lift because at some point that next spike could be very dangerous and could cause case failure inside the chamber.
You can also see bullet shifts with harmonic changes as well due to bullet leaving the barrel in either an up or down whip action to harmonics.

 

[FeMan]

I agree with James. But to answer your question about wind affects, a 9 o'clock wind will drop your point of impact somewhat. However, you shouldn't notice it unless the wind is variable.

 

[CharlieNC]

Bullet moved down because of harmonics, and not necessarily with an accompaning velocity explanation. Bet the horizontal also shifted direction in that powder range?

 

[500Stroker]

Bullet moved down because of harmonics, and not necessarily with an accompaning velocity explanation. Bet the horizontal also shifted direction in that powder range?

Yes,it did

 

[Zero333]

Barrel Harmonics. All part of the testing game. The farther out you do the ladders the more likely you're going to find such a node.

Barrel is vibrating/whipping and bullets leave the muzzle at different points of the muzzle whip. The higher powder charges that should of landed higher but went lower, did that because the muzzle was at the bottom portion of a whip (muzzle pointing down).

Theory is to find the powder charges that leave the muzzle when the vibration harmonics are farthest from the muzzle (closer to the receiver end). Vibration harmonics travel like a wave the length of the barrel continuously back and forth.

Here is a link to a good read...
http://www.the-long-family.com/shock wave theory summary explanation.pdf

 

[CJ6]

Tuners....

 

[johnmyers]

Recently on a windy day a shot powder ladder for my 6BRX with SMK 107 bullets, Varget and BR-4 primers. My powder spread between loads was .2 grain all seated .020 off the lands.
The powder ranged from 30.2 to 32.5 gr every .2 gr, looking for the correct powder node for an accuracy load.
At first everything went as expected with the shots lining up vertically as bullet speed went up with more powder the shots went higher. Until I got to the middle of the powder range around 31.5 gr all of a sudden 3 shots went lower then the prior lower grain weight load ?
Is this common?
Could have the wind blowing left to right somehow blown them down ?
Has anyone seen this before ? Why ?
Thanks in advance for the comments.

I have had this happen before and when they went lower I was getting close to a good node. It seems strange when they go faster they shoot lower but it happens