Fouling residue build up (copper and burned powder deposits) occur with EVERY shot, so cleaning after every session is important. In fact, with some rifles and loads, accuracy can be effected after just a few shots. You should swab all oil from your bore before shooting as excess oil in the barrel can increase pressure. Also be sure you know whether your solvent is one of the more aggressive types as these cannot be left in the barrel more than ten minutes. Follow directions for the particular solvent that you are using and you'll be alright.