I think you will have a hard time finding any factory ammo that doesn't vary by up to 5 or so grains in a given box.
I weighed some Federal premium ammo in 7mm Mag, loaded with 150 grain bullets. The variance was about 6½ grains from lightest to heaviest.
Just for the heck of it, I shot a couple of groups with this ammo in a very accurate M700. It shot very well indeed.
The primers backing out is usually caused by light loads, not heavy ones, and not by improper seating initially.
And the comment about 3 grain of bullet weight pushing you over the pressure threshold??? I guess not in any real world situation.
Somewhere there seems to be a lack of understanding of the basic concepts involved in factory ammo loading.
Regards, Eagleye.