My Prosport has always been fed on a diet of JSB's and AA fields, as have most of my rifles for the last couple of years due to a huge stock of pellets from my FT days.
I have now run the stock dry and am now in a position to start the laborious task of testing other brands of pellet (wasn't unhappy with either JSB or AA though) i was in the local gun shop and thought I would throw caution to the wind and buy some superdomes.
Well, I tried them tonight and they have transformed my very tame and well mannered rifle into a nasty, twangy, inconsistent rifle.
Lesson learned! Stick with known quality ammo.