Pitting on the outside of the barrel is of no consequence, it is the condition of the bore that matters. .22 rimfire ammunition is both self-cleaning and protects the bore, this technology going back to the 1920's. Your BSA Supersport was made in the 1950's and the bore should still be fine. Sadly, magazines for the Supersport are now very hard to find but the rifle still has some collector value. If you can find a magazine then you will find the Supersport to be a very well-made and accurate rifle.
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