I have a Benjamin Prowler that has been a non-shooter since I got it. I never hit any of the house sparrows I aimed at, and while all that could be the shooter (ME), I can hit them with my wood stock 760 from the 1970's with open sights so I got to thinking that I had a problem with the scope?
I swapped out a new Simmons 3x9 for a 1985 Simmons 3x9 and the group moved as one would expect but the groups remained at minute of cantaloupe at 30m. Very ugly shooting indeed. I changed out pellets, heavy, light, JSB's, Diablo's from everybody I could find, even Daisy and Crossman just to see if I could get a shooter... nope, all shotgun patterns.
(My impromptu indoors 'bench rest' setup)
Out of frustration and desperation, I decided to lap the bore with a good cleaning first followed by a good patching with FLITZ to see if I could shrink the pattern without opening the bore. The bore was much more filthy than any front stuffer I have ever cleaned! Lead remover, straight Ammonia, Ed's RED, HOPPES, bronze brushes and a hundred patches later, I got a clean patch and started a FLITZ patch.
I frankly could feel the burrs catching the patch, it felt like cleaning a concrete sewer pipe and not a barrel! I worked a half dozen patches with a touch of FLITZ, cleaning after each scrubbing and drying the bore with dry patches. The last patch ran smoothly down the bore, all the way to the crown and much to my delight, came back without snagging any burrs.
After a good cleaning and a wet patch of tranny fluid followed by a couple dry patches, I fouled the bore with a single shot and sent five down to the trap. I will probably never see a group like this one again from this gun and its far from seasoned so it may open WAY up over time but I got a 1/2" group at 30 meters inside my home (I have a 70 foot long house with four levels, offset with 6 stairs to each level and an attached 4 car garage, giving me 120' of room from wall to wall through the doorway) and just wanted to share it before I get back to making holes in another target.
12mm or 1/2" group using JSB 15.89g Match Jumbos