If you weighed all your bullets, there should not be a problem. I have seen lighter and/or heavier bullets in the same NEW box of bullets.
I would suspect your Bi-pod.
Shooting off a bi-pod on a HARD surface will cause you the problems you are experiancing.
The bi-pod is fine if in soft earth but, NEVER off of a hard surface. A bi-pod will destroy a good group almost everytime if your not careful.
The Vern Junkie machine would not be needed for the shooting you are doing.
For the hard core benchrest shooter, yes it is used.