Accuracy issues: Equipment, technique or both?

[Drifter]

All off of a Harris bipod on a concrete bench, but adjusting POA by sitting position (i.e. no sandbags at all).

FWIW, when chasing for the best possible groups, a bipod on concrete wouldn't be my preferred method. It potentially makes the rifle more temperamental, requiring a firmer hold to maximize results. A bipod will tend to bounce on a hard surface, and it can be difficult to load the bipod in the exact same manner each time. POI shifts compared to other methods and / or from more forgiving surfaces are not uncommon.

That being said, one should test a weapon in the same application as its intended use, or in the manner that the shooter prefers. But sandbags front and rear from the bench would likely provide the best opportunity for tiny groups, and works best for me for load evaluation.