Hi spl82
If your gun was shooting anywhere close to the typical 600 fps - you'd expect 25 zero to 30 yd target drop of only about 0.5 inch.
Did quick 'play' with Chairgun and, even at only 400 fps, drop should be ~1.6".
Above assumes your scope centreline is around 1.5" above bore centreline.
Something's wrong somewhere.
Are you shooting at paper targets or live quarry? If former, does pellet leave hole or just an impression in the target? If shooting at bunnies, do they catch pellets and throw them back?
Suggest you get yourself/gun to a chrono with haste.
Biggles