The accuracy of my stainless/synth. Ruger .308 has deteriorated markedly .. I'm getting a lot of fliers which spreads the groups to around 3" at 100yds.

The barrel has only had a few hundred rounds

The only thing that I can think offhand is that by floating the barrel the flex in the forend may be the causing the problem.

Could the flex be a problem when shooting off the bench?

Cheers,
DBT