what is the problem with brass brushes

bronze brushes will eventually damage firearms barrels to if not used correctly,i would never put anything but soft fabric patchs thru not only my much loved 20year old air arms pcp rifle but none my others as well.as you said air arms recommends cleaning approx every 250 shots,i have never found that necessary,i dont clean barrels now unless i notice accurracy dropping off and evan then i dont remove all the lead fouling from barrels because you then need to put quite a few shots thru to lap barrel out again to have accurracy return,i never put a bronze brush thru my 22lr rimfire rifles either for exactly the same reason,you can over clean barrels too,high velocity center fire rifles copper foul their barrels and if not removed this will destroy their accurracy too,i have purchased qiute a few high powered center fire rifles their owners believed the barrels were shot out because they hadnt cleaned the copper fouling out fully,that all shot brillently when cleaned properly,i have fired many thousands of high velocity lead bullets out of firearms with excellent accurracy once i had removed all the copper fouling from barrels,i would never use the copper plated pellets now around thru any of my pcp rifles or pistols because the copper will build up and foul the barrel and its a real hassel to remove from soft airgun barrels without possibly damaging the barrel,and lead pellets will never be accurrate out of a copper fouled barrel,and the same applys to lead free pellets and those with synthetic sabos in airguns,so hopes this helps its not that complicated once you understand why these things happen.