I bought a Limbsaver de-resonator, the one for heavier barrels (they make two sizes) and hung it on my 26 inch Criterion heavy varmint barrel in 223.

Instructions say to start with it about 1/2 to 3/4 inch back from muzzle (with a free floated barrel) and fire two shots, then continue firing two shot groups while gradually sliding it back and stop where the groups tighten up.

I watched the vertical spread go completely away and turn into a small horizontal spread. So I can report that it does indeed work, but I have not done any more testing since that first outing.