FX Power Pup .30

Hello, I've had the FX dreamline power pup 22cal for about six months now and it shoots 18 grain jsb pellets wonderfully at 50 yards printing 3/8" to 1/4" groups with no wind I'm very happy with that but I'm just starting to shoot slugs and not having great success I was curious if anyone has had experience with this set up and if so could you please share what you've learned. I have tried various types and weights at different speeds and regulator pressures but cannot get better than 1 inch group at 50 yards. I'm very new to shooting slugs but I have watched many different videos trying to learn everything I can to improve by grouping I'm starting to wonder if 1 inch at 50 yards is the best I'm going to get if anyone has done better please share information I would greatly appreciate it