I built a cider press years ago when I was in High school. Hooray for wood shop class!. We pressed a lot of cider on it over the years. The press was fine but the grinder was manually operated. We averaged about 2-2.5 gallons of cider per bushel.
Later when making cider on a commercial scale (250 gallons a week), I noticed two tips to increase production. First, always squeeze warm apples not cold ones. Apples that are at room temperature will give more juice than those pressed cold from the cold storage room.
The second issue is the grinder. A commercial hammer mill will grind up the apples so fine that they are almost like applesauce when they feed into the press. A manual home grinder just doesn’t grind find enough to extract the same amount of cider per bushel. If I recall correctly we got 3-3.5 gallons of cider per
bushel squeezing commercially. It does depend a bit on the varieties used and how dry or juicy they are as well.