Fire lapping won't hurt, and may help. Three inch groups are perfectly acceptable for a hunting load if that's at 100 yards. But we all want better if we can get it.

When you tried Triple Seven and Pyrodex, was that with pellets also? If so, I would get a jug of loose Pyrodex RS or Triple Seven and try loads in five grain increments from 80 to 110 grains. I'll bet you get the best groups with something in the 85 to 95 grain range. Also, you didn't mention what bullet you are using. You may want to get some 300 grain XTPs or Deep Curls and Harvester H5045SB sabots and give them a try. Those bullets shoot well out of most of my guns and are the best shooting bullets in my Mustang. Mine is not a tight shooting target gun either. My best loads get me groups in the two inch range at 100 yards.