Powder charge increase sensitivity

[fuzz]

In my 358wins I have worked with six powders for various loads. All of them gave consistent temperment when approaching full loads. Then I tried Varget. On two occasions when working up, a starting load gave a wide ES, next grain up, less ES at avg. 2150fps. A half grain more gets me 2250 with a decent ES.
A hundred fps for half grain. Makes me think. I am aware of lulls and then some "catch-up" as charges increase, but this catches my attention.
An explanation by the knowledgable would be much appreciated.
Thanks
Dwayner

 

[Ganderite]

Powders only work well when used in the correct pressure range. Your start loads might be too mild and pressures are too low to burn reliably. That kind of powder can do poorly at 40,000 psi and be steller at 55,000.

be aware that "identical" rifles can have a difference of 10,000 psi with the same ammo. So pay more attention to your rifle than the book. But the Chrony gives a good idea of pressure. there is no free lunch. iI your velocity is over max, so is the pressure.

If the poor ES loads were low velocity, you can be sure it is just a too low pressure issue.