Choosing accuracy node

[GSPV]

Positive compensation (snip)

It's based on a load's velocity spread versus muzzle angle on exit.

Close.

The bullet goes where the muzzle points when it exits. Period.

Velocity, which we measure after the bullet’s exit is just a handy stand in for bullet exit.

Not a load's average velocity that changes average POI change.

I never said that it did...

I’ve gone out of my way to emphasize that it is where the muzzle is pointed when the bullet exits that matters. Velocity is just a stand-in for the exit time. That is, if velocity is noticeably greater, we assume that the bullet exited quicker.

It only takes a few *tenths* of a grain to see the effect on paper.

And, I assure you, everyone that shoots a 6 PPC or similar at 100-200 yard benchrest understands this and knows that they have to change their powder charge as the day warms up.

 

[dkhunt14]

Close.

The bullet goes where the muzzle points when it exits. Period.

Velocity, which we measure after the bullet’s exit is just a handy stand in for bullet exit.

I never said that it did...

I’ve gone out of my way to emphasize that it is where the muzzle is pointed when the bullet exits that matters. Velocity is just a stand-in for the exit time. That is, if velocity is noticeably greater, we assume that the bullet exited quicker.

It only takes a few *tenths* of a grain to see the effect on paper.

And, I assure you, everyone that shoots a 6 PPC or similar at 100-200 yard benchrest understands this and knows that they have to change their powder charge as the day warms up.

It is pretty obvious Bart has never shot many ladders at 1000. In some cartridges like the Dasher a few tenths can be a completely different node and way higher or lower impact. That few tenths in a Dasher is typically about 10 fps per tenth. Matt

 

[urbanrifleman]

Have you seen this? One either side of the node at 29.9 and 3323 the upper and lower charge (29.6 and 30.2) are 3307. A true velocity node. Vertical is constant.

 

[GSPV]

It is pretty obvious Bart has never shot many ladders at 1000. In some cartridges like the Dasher a few tenths can be a completely different node and way higher or lower impact. That few tenths in a Dasher is typically about 10 fps per tenth. Matt

Matt,
There is a subtle bias of short range in my explanation above.

But, that short range is much more tolerant of ES/SD than long range actually supports what I’m saying.

And to reiterate for folks coming in late, what I’m saying is:
1. The barrel oscillates like a tuning fork when the shot is fired.
2. The bullet goes where the muzzle is pointed when it exits.
3. There are inevitable little differences in when the bullet exits. Variation in powder charge is but one cause of those differences.
4. Tuning, by powder charge or with a tuner, such that the barrel is on the upswing when the bullet exits helps whitewash over the differences in when the bullet exits. Conversely, tuning (or failing to tune) such that the barrel is on the down swing when the bullet exits aggravates the differences in bullet exit.
5. A way to see that the barrel is on the upswing is showing that the POI moves down the page with increasing powder charge.

This is all well-known stuff. I didn’t come up with any of it. None. Nada. I’m merely sharing the wealth.

(Keep in mind that I don’t shoot 1,000 yard, I have a short range bias)

 

[mikehotel]

thanks for the discussion,

 

[Bart B.]

Post 20 edited, "slower" replaced "faster."

My error.

 

[Bart B.]

5. A way to see that the barrel is on the upswing is showing that the POI moves down the page with increasing powder charge.

Except when bullets leave right after the muzzle axis was starting on the upswing just after the muzzle axis was at the lowest angle. Then faster bullets will leave on the down swing.

 

[GSPV]

Except when bullets leave right after the muzzle axis was starting on the upswing just after the muzzle axis was at the lowest angle. Then faster bullets will leave on the down swing.

Dude, you are obdurate.

I’ve already told folks, at least those that are trying to understand, that they want to stay in the middle of the “good side” and that the groups will become dots as the graph approaches the bottom and then blow up. Everyone that shoots shortrange BR knows this from experience.

 

[dmoran]

@Bart B.

Below is a screen shot of a 2-shot pressure trace test, from 2-loads with the same charge and nearly the same velocities (9-fps spread), that have a difference of 0.12-m/s in bullet exit times.
The load/tune difference between the two was these 3 things:
- 0.002" in seating
- 0.0015" in neck tension
- a difference in neck prep between the 2 cases
The blue trace had a bullet exit time of 1.22-m/s @ 14868-psi <> muzzle velocity of 3033-fps
The red trace had a bullet exit time of 1.34-m/s @ 13026-psi <> muzzle velocity of 3024-fps

​

 

[Bart B.]

And anywhere on the upswing is not good. It has to be such that the angular spread of LOF compensates correctly for the bullet angular drop spread. The muzzle axis vertical swing rate is not linear over time.

 

[GSPV]

@dmoran:

That’s excellent stuff!

@Bart B. I’m putting you on ignore.

 

[Bart B.]

@dmoran:

That’s excellent stuff!

@Bart B. I’m putting you on ignore.

You cannot handle the truth.

 

[Bart B.]

I’ve already told folks, at least those that are trying to understand, that they want to stay in the middle of the “good side” and that the groups will become dots as the graph approaches the bottom and then blow up. Everyone that shoots shortrange BR knows this from experience.

What if the middle of the good side has the bullets departure angle spread greater than what's best for correct compensation for bullet drop?

 

[Had2muchofForums]

@GSPV

Good stuff, thanks for the visuals!

 

[GSPV]

@GSPV

Good stuff, thanks for the visuals!

You’re very welcome.

Just trying to repay the community for what it has done and keeps doing for me.

 

[Link]

Ok I have read the above at least 3 times. Nothing there looks like the ladders I have shoot. Can someone decipher my ladder at 300 yd in layman's terms? thanks

 

[Bart B.]

Looks great. All three main level are virtually equal accuracy wise.

It's possible to have near equal accuracy across a 2 grain span of average charge weights for some cartridges.

Prove this by repeating the same loads.

 

[dmoran]

... It's possible to have near equal accuracy across a 2 grain span of average charge weights for some cartridges.

What calibers have you seen a 2-grain spread in charge weights to yield equal accuracy potential?
And to what kind of accuracy potential?

 

[dsculley]

Link,I see 2 nodes there. Shots 1 & 2, swell as shots 5 & 6. I would use 30.7 and test for seating depth if you haven't already. Then load 20 rounds & test at distance.

30.6 & 30.8 have nearly identical vertical.

 

[hottotrot]

View attachment 1055014 Ok. Here is the better graphic.

Vertical POA is always the center of the three horizontal lines, but advances by one vertical line per shot.

Each time I advance to the next POA, I am advancing my tuner (which is like changing powder charge) by a small increment.

You can easily see the graph make a sine wave.

So the "good side" would be bullet holes #3 and #10, as numbered from top to bottom or left to right? These would be the loads to develop?

Also, do you have any examples of ladders shot @ 600y with the same loads? I'd love to see how the two methods compare visually.