You really need to experiment with different powder charges and different bullets. For example, I never was able to get decent accuracy with Triple 7 pellets - best groups I ever got at 100 yards were 5" or so. Switching to loose powder decreased my groups size by a lot.
Some guns are finicky and even a difference of 5 or 10 grains of powder can make a big accuracy difference. Also, with Triple 7 you usually need to swab the barrel in between shots. Trying a different powder all together might help too....