Scratching my head at the range with different powders

[Harry Knutz]

It's due to the barrel harmonics and the direction the muzzle is pointed when the bullet exits the barrel.

This!

 

[Philward]

Shot these the other day, 257WBY 115g Nos BT 3.210 coal. Same charge of powder but the red was Norma MRP and the green was IMR 7828. No idea of velocity since chrono is broken. But the powders are essentially the same in the burn chart and both manufacturers have the same charge weight range for each.
Fired the MRP first 3 rounds which were the high and left one and then 2 right on top the orange bull(the 2 orange spots). Then fired 3 7828 at the shoot and see target, first shot to left of center and the next 2 up in the white paper. Followed up with the last 2 of each string, taking a short break between each shooting. Just to show difference in POI with different powders, all else the same. Cases are once fired, annealed, sized, necks turned. Nosler data says 3400 velocity with 7828 at the charge weight I used.


MRP is heavier by volume than 7828.
Norma lists relative Velocity and relative pressure for powders, MRP being RV 89.9, RP 80.1, 7828 RV 84.3, RP 77.5. I think it's relative to IMR4350 which in the chart is the 100.0 point, so MRP should be slightly more pressure and slightly more velocity than 7828. I was using standard 7828 not 7828ssc.

 

[waveslayer]

Faster rounds will impact lower with less "drop" and all the harmonics being different

 

[sxssixteen]

Yes, it does have much to do with barrel harmonics. I had it explained to me a different (still related) way. A faster bullet gets out of the barrel earlier in its vibration curve (whip), while a slower bullet exits the barrel later in the vibration curve. As the barrel whips, it throws the bullet higher on the target. Of course, all this is in microseconds, but it makes a difference in bullet impact.

 

[BrentM]

sorry for asking an elementary question, thanks guys for the answers!

For real? I was answering the question with non-elementary information so you could better understand why impact points are not tied to velocity. I discovered a lot of this issue when shooting ladder tests at 500 and not understanding why a slower speed/charge would often be high or in the group of other faster charges. Dug into barrel time node and harmonics to help address tuning issues I was having back then. I don't shoot traditional ladders anymore because it takes to long to tune.

 

[powermax]

For real? I was answering the question with non-elementary information so you could better understand why impact points are not tied to velocity. I discovered a lot of this issue when shooting ladder tests at 500 and not understanding why a slower speed/charge would often be high or in the group of other faster charges. Dug into barrel time node and harmonics to help address tuning issues I was having back then. I don't shoot traditional ladders anymore because it takes to long to tune.

thanks for the answers!

 

[Old Rooster]

I did not pose the question but have experienced the same thing.
Enjoying everyone's hard word and results.

 

[Aoudad 101]

Faster = flatter