70 odd years of grot may take some shifting! I wonder how many BSA's get any sort of barrel cleaning at all?? Not many is my guess. And it only take one patch of rust or one area of sticky dirt up the bore to significantly reduce accuracy and velocity.
Dont forget you can start the process off without waiting for cleaning rods. You can use cotton parcel string with a couple of big (.177 sized) knots in. Tie the knots in one end (one after the other) and add a small narrow weight to the other and pass the string (weight first) down the barrel until you can grasp the end, then a couple of drops of oil on the knots and pull them steadily through the barrel, If you have a phosphor bronze brush, then that can be tied to the end as well. If you cant find cotton parcel string, then fishing line witha couple of lead split shot nipped onto one end to provide weight is good, Tie on a small bit of cotton sheet. or J cloth (it needs to be a fairly tight fit up the bore) and pull through. Check out the colour of the emerging cloth - it will surprise you I am sure
Good luck and post up your findings to put us all out of our misery


Good luck.......