I built one many years ago, and through use I found a few things that work well.
#1 Two stage pump A MUST.
#2 A Tall wedge 10 to 12".
#3 Wedge cutting edge to be on an angle, rail side closer to the wood then the top.
#4 Pusher needs welded piece to capture the wood. I used a 4" pipe 1/4" tick. Split in1/2 and welded to the pusher. If the wedge is mounted on the cylinder, then the pipe pieces are welded to the plate.