I'd like to see scientific data on which modifications are the most effective at shrinking group size. If I had to guess, I'd put them in the following order for the Axis:

1. Trigger
2. Comb height
3. Barrel
4. Scope and mount
5. Bedding
6. Stock composition
7. Paint color

These are factors organic to the rifle, so I've not included "handloading", though that's a popular suggestion.

I unashamedly modify the triggers and combs of rifles that don't meet my needs before they even get to the range. Those are easy to pick up on without firing a shot, much like the flexible forend and wrist. It's also a cheap and easy fix, especially if Rockite is used.