.25 Hunter Magnum Extreme question

[Dragonscout]

Just getting into larger bore as I recently retired. I'm breaking in a Hunter Magnum Extreme .25 and have only around 40 or so shots in the bore so far. I'm waiting on the trigger screw kit from Airgun Detective to ease up this atrocious trigger, although the USPS seems to have lost it. Put a low end 4-16 scope and so far at 25 yards I'm averaging quarter to silver dollar sized groups with the factory Gamo competition pills. Problem with the factory stuff is the lack of skirt concentricity. Two or 3 fit ok then a loose one then another couple of fairly tight rounds have to be playing havoc with the actual grouping. I figure from what I'm reading it'll take 100 or so rounds to break her in. I have some JTS pellets but I'll just use up the Gamo stuff first. What insight can you give me if you have the time? I do know this thing makes a  loud "thwak" when it hits the woodpile! Thanks for your time and insight in advance, jerry