I am trying a set of Remington cases that I have uniformed the primer pockets and deburred flash holes. Trying to get rid of some higher standard deviation numbers and maybe a quarter inch closer grouping. These were loaded with a Lee C309 same loading that produces typical 1 1/2" groups with this bullet in this gun. For some reason the groups were more in the 2 1/2 - 3" range after the deburring. I think I'm going to have to adjust the load after deburring the flash hole. Standard deviation were lower, so speeds were closer to the same. Does anyone have experience with this? Is it common for the flaring of the deburred flash hole to cause a change in the burn of the powder, pressure, (or as Glenn would say the RPM) etc causing the groups to spread?