Point of Impact DROPPING as Velocity Increases?

[David Christian]

It falls away again from 6 - so loading between 6 and 8 is also an option ?

Yes, only if it wouldn’t have ruined my brass. Those speeds were too hot!

 

[J_idaho]

I would retest farthest spreads and see if the rifles poi has moved or if it’s the load. I would guess it’s not repeatable.

 

[RabbitSlayer]

My 100 yard testing has also found that more velocity doesn't always mean higher poi. Im going with muzzle exit timing, but I dunno.

 

[SSL]

My 100 yard testing has also found that more velocity doesn't always mean higher poi. Im going with muzzle exit timing, but I dunno.

Got my vote. It just so happens I was testing powder charges for my .243 today and kept this thread in mind. Without saying what powder or bullet weight I was using so as to not encourage someone to just jump right in without performing their due diligence, I went from 44.0 to 46.5 grains. and the center of my groups moved downwards (though quite gradually) over the range of my testing. The final load printed just over an inch lower than the first (44.0) load, but in a nearly straight line down (no left-right variance).

 

[222Jim]

My more pressing question is why are you doing load development for 100 rounds when your average is already 0.23 moa. Save that load and barrel and go win matches

Simple reason..............I got lucky first day out and landed on a great load.

 

[davidjoe]

OP, I think your results actually prove those explanations you read are valid. We have to keep in mind that the closer the target is to the muzzle, the less that all differences in velocity from shot to shot correlate to a change in point of impact. But, gravity’s effect over time of flight is a law, and what you had read are the only explanations, - the faster shots weren’t “aimed” at the same spot.

Looking at the illustration I borrowed from the internet, it is easy to envision certain effects when walking the target back closer and closer to the muzzle; all elevation differences from even wild velocity variances in ammo still converge at an origin point (muzzle), where they overlap completely at the beginning, and deviate slowly but increasingly from there.

Take David C’s result above with 3.5 grains and ~150 fps difference virtually sharing drop between extremes. We must expect and agree that whatever the 100 yard target shows about a 3+ grain lower, slower charge striking similarly, in actuality no one can drop 3 grains of powder and 150 fps and expect the two shots to hit anywhere close together at 1,000; if they did, weighing charges precisely would not matter.

If we take David’s vertical delta between his first and last shot at 100, and multiply it by 10, it still remains an immaterial distance, but JBM puts the slower shot 2.7 moa lower at 1,000, well beyond positive compensation. But he only needed a tiny amount of positive compensation for close range shots to share p.o.i. (He has a lot less than yours, which stands to reason because of the barreled actions’ differences).

At 100, the differences in expected drop between test velocities is small but real. The only possible explanations are harmonics, handling or the environment.

 

[358WCF]

My 100 yard testing has also found that more velocity doesn't always mean higher poi. Im going with muzzle exit timing, but I dunno.

Yup. I've seen this at times too. It defies gunlore logic. Does it repeat?

 

[AlNyhus]

Yup. I've seen this at times too. It defies gunlore logic. Does it repeat?

View attachment 1640569

Most gunlore ignores the fact that barrels move when fired. If they didn't move, any old charges of any old powders would show show the same accuracy on target.

Managing barrel movement is what we're doing when we 'tune'.

Good shootin' -Al