Judging by the brass deformation, and the Ironing of the crimp, You are way overpressure. You will need to back off more than just 2 grains. The accuracy sounds very good, but you should get the load pressure tested after you back off. Tom Armbrust at Ballistic Reseacrh can test them for you. I would guess you current load is around 15K PSI maybe a touch more.
Please be careful. Maybe try IMR 4759, I use it with a 605gr slug at get high velocity and low pressure. My load uses 64.0 Gr. of IMR 4759 and gives 1555 FPS @ 11,400 PSI
Greg