Hello Birdslayer. I got off to a rough start with my .22 Streamline, but did eventually start getting what I consider excellent accuracy from the gun. In my case, I was getting decent groups from the 15.9 JSBs, but horrible groups from the 18.1 JSBs. By taking chronograph readings at 50 yards, this was tracked down to a stability problem with the 18.1 pellets. Extreme spread at 50 yards with the 15.9 JSBs was around 30 fps, but much greater than that with the 18.1s. It seemed the Smooth Twist barrel was providing very marginal stability, at least with the heavier pellets. I tried cleaning the barrel, with no improvement, so decided to stop cleaning the barrel altogether. Just as with rimfire shooters, many airgunners find that accuracy improves with a seasoned barrel. That seemed to do the trick. Accuracy improved until after shooting a couple tins through the barrel without cleaning, half inch groups at 50 yards were the norm with the 15.9 JSBs, and the 18.1s were not far behind. It is my understanding that a lot of people have found that their Smooth Twist barrel needs to be shot in to obtain best accuracy. That was certainly the case for me.
At this point, I can count on moa or better accuracy at 50 yards under low wind conditions. To verify, I just shot a couple groups today at 50 yards in the rain using unsorted 15.9 JSBs. Both groups measured 0.52", which I consider typical for the gun, although it is not unusual to get groups measuring 0.04" or less. I have not shot extensively at 75 yards, but groups at that distance typically range from 0.78" to 1.02". Wind seems to be a much bigger factor at 75 yards. I would think your Impact would provide similar accuracy. What groups sizes have you been getting?
When I am intent on getting the very best accuracy from my rifle, I do sort the pellets for weight to make sure I am eliminating that variable. I also single load, and use lightly lubed pellets. Since I am not cleaning the barrel, the lube is mostly intended to prevent excessive leading. Although hard to prove, these additional steps seem to improve accuracy a bit.
Chuck