I've seen it happen at the range and wondered what I was doing wrong myself. Your best bet it since your shooting open sights, adjust your sight picture. Going from a 6'oclock hold to a full cover can make all the difference in the world as long as you remember which is which.

As for raising the power of the powerbelts, some of those kind of rounds don't like it. I have heard both ways but never experienced any great accuracy with them with over 100 grains of powder. Especially shooting Triple Se7en. Of course I do not shoot pellets. Maybe a slight increase in pellet amount will not send them wild.

One thing to make sure you are doing since your shooting Triple Se7en powder is pull that plastic button on the bottom of the powerbelt before shooting. You will see a small plastic spike down there. Put a dab of bore butter, lard, oil, even spit on that spike and then replace the button. For some reason, and I suspect the extreme heat that is generated by Triple Se7en in comparison to the other powders, the powerbelts like to hold onto that button longer. This bore butter on the spike will help them shed the button faster and make the shoot a little flatter. At least it did in my case.

I shoot a 245 grain Aero Tip with 100 grains of loose Goex 2f and the accuracy in my Staghorn is outstanding...