Are you shooting too rapidly - causing the barrel to overheat? It doesn't take much to overheatyour soft extruded Spanish barrel.

Are you swabbing with a patched bore brush that removes groove/rifling crud easier than a jag?

I'm assuming you are using two pellets. Buy a pack of 30-grainers & mix them....trying 80, 90, 110 & 120 grains.

When all else fails..... switch powders (preferably loose)& bullets. The el-cheapo T/C Cheapshots fly real well & punch a nice hole. A couple of posters elsewherehave harvested deer with them beyond 200 yards.