OSH makes a point---I'm gonna guess you'll be in the realm of 8" drop at 150, but this is easily helped out by sighting in high at 100yds (say, 2 or 3").

Sorry, overlooked your other question 'why won't my gun shoot well at 80'. Well, the gun chooses the load it will shoot well. A gun might shoot well at one charge with a certain bullet, and then 5 or 10gr away, it just ain't gonna feed the bullets out quite right. Now, if you try different bullets, you will probably find one that your gun will shoot accurately with a heavier charge. But, as MDevil will tell you, powerbelts are better shot slow than fast when it comes to terminal performance. They're soft, which is great for low-velocity performance. Give the bullet credit--a bullet that big doesn't hafta be going fast to do serious damage.