Impact plenums.

I'm using both, the one Michal copied from me and the one I copied from Mr Rowe (M14 threaded). The one from Poland is the best for looks, value and performance. It's more than enough unless your going to do more mods for .30 and larger with heavy slugs. In .30 cal with a 700mm barrel I had 90cc total plenum and topped out at 132 fpe using a 1/4" (6.35mm) valve. Increasing the total plenum space to 160cc did not increase performance because of the valve restriction. I'll install a 7mm valve with a PEEK seal soon. That should make around 150 fpe on 150 bar. I never go above 150 bar anymore.

You really need to optimize the airflow path by reducing restrictions to get the most out of a large plenum.