http://www.powerbeltbullets.com/docs/PBB28inchballistics.pdf has this for thedrop with 150 yard zero using 100g of 777, you were using 80:

If you know the MV of your load we can drop it into here:
http://www.sav10ml.com/pages/load_data/traj_basic_dat.html

According to this chart you with 100g of 77 you need to be 5 1/4 inches high at 75 yards to get the drop in this chart. I am gonna say with 80g you bullethas the drop of 200 yards at the 175 yard point. So according to the chart you should have been-11.5 inches low at 175, which was about what you were.Anyway if you have a chrony get the ML and we can figure it outpretty close, range tests like your doing it the best. shoot 3 shots.
Chap