That's a lot of powder you are putting under a Powerbelt. I shoot a CVA Staghorn Magnum which your rifle replaced. When I shoot a powerbelt I shoot 90 grains of loose powder. I would not even worry shooting a deer at 100 yards with that load.

If you're sighted in for only 50 yards, you can expect some definate drop in the powerbelt. Actually a trip to the range would be in order but 3 inches would not surprise me. I sight my scoped rifles in for 70 yards. That way they are a little over an inch high at 50 yards and almost 2 inches low at 100 yards. So it is a matter of what part of the kill zone I aim at. At 50 yards, I aim for the lower center and at 100 yards I aim above the center.

If you think there is a chance you might have to shoot out to 100 yards might I suggest a trip to the range and try some shots out that far. Again, 150 grains is a lot of powder.... Good luck with your hunt.