Are you running at full PTO speed? Some people don't like to run equipment at full speed. Your manual should list the plunger strokes per minute at full PTO speed. 80 plunger strokes/minute divided by 12 strokes/bale = 6.6 bales per minute or 400 bales per hour (gross rate at 100 percent utilization).
Look at how much time your baler spends running empty or stopped in one spot. Then try to keep it moving more to make more bales per hour. There can be a lot of run time lost for: turning on ends and traveling between windrows;
waiting for empty wagons;
lighter than ideal windrows;
down-shifting and up-shifting for hills and inconsistent windrows;
re-tying missed knots;
replacing shear pins;
unplugging the pickup;
A 50 to 60 percent utilization (up-time) should be realistic pulling a hand stacked bale wagon. Operations that drop bales on the ground and use hydrostatic transmissions to keep the baler near full capacity might achieve 80 to 90 percent utilization.