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How many more shots you can shoot after polishing depends on how rough the barrel was to begin with. If it was rough and fouled in 100 shots, a proper polishing job could extend that interval to 1000 shots.
It also depends on the alloy of your projectile. If nearly pure lead, such as JSB uses, then cleaning is fast and easy. If high antimony hard projectiles like Crosman are used, then cleaning can take a lot longer.
If you could shoot 2000 shots before you started getting fliers, then you may not get 4000 after polishing, as 2000 is already pretty good. So, the rougher your barrel, the more polishing will help it. Of course, if the roughness is so deep that you projectiles are loose after polishing to a smooth surface, then you have a no-go. Ditto for such shallow rifling that it is gone before the barrel is smooth. Hence the value of using a "hard lap". A lap cast in the bore will not preferentially cut the lands, or over round their corners. This can happen when you overuse a soft lap, even when fine polish is used. Many will tell you that over polishing is a myth. Perhaps for normal barrels, rather than very rough ones. You just need to know when to stop.
Big bore projectiles may foul more and benefit from some sort of lube to reduce that, and make cleaning easier. So, you may need to be more specific about your platform, your experience, and your expectations.