My 124D that is fitted with Pro Mac Kit shoots about 75 fps faster than the one with factory spring, however I just removed open sights and fitted a 4-12 Hawk scope to the factory sprung 124 and gun is dead nuts accurate just like the higher velocity 124D. I set target at 35 yards and both the 7.9gr and 8.4 gr JSB exacts are all on top of each other.These 124's are incredible. I always wanted one and now I have two.