Its true what you say about some bolt actions being finicky. I have tried all sorts of loads in my 458 Lott ,trying to get 300 gn bullets to hit in the same spot as 400gn bullets and hopefully close to 500 gn bullets. The 300s are hitting way way higher than the 400s and more again than the 500s ,even going up and down in powder charges. I suppose ,having heavier barrels as on a double might make things closer. I hope so ,as I am getting a double some day and would like to have lighter practice loads as you did.