I have shot a BPS for over 30 yrs, (I own 4) one of the most important things to remember is to keep the barrel clean where the shells slide into the barrel. I have found the best way to clean that part of the barrel is first take the barrel off and mount a brass bore brush(what ever gauge)on a high speed drill motor take some gun solvent dip it in solvent work it in and out several times of the barrel while the drill is at a high speed, keep your brush wet with solvent,this will cut the crud out that you can not polish or clean out good enough by hand, be sure to clean the solvent out of your barrel and only put a very lite coat of oil back in the barrel. If you have never done this, you will really be surprised at the differences you will see the next time you shuck a shell out of that gun.
I hope this tip will help you and be sure to pass it on.
Dogs are only as smart as their handler