When using smokeless, a plastic gas check should increase velocity by a good margin. With black powder loads, one should not use plastic as it will melt onto the bore and fill the grooves - in places.

Brass cases will of course demand only card and fibre as a 19 or 18 gauge wad will be needed to fill the case due to the thin walls. Trackofthewolf (Circle Fly Wads) has all sizes of wads.