In general I polish before shooting the first round. It is my way of breaking in the barrel. There are others that have their own special way of breaking in a barrel and still others that just shoot it (no break in). It is never too late to polish a barrel. If you do decide to polish, just make sure all of the powder and copper fouling is gone, other wise, you will be polishing the copper residue and when it is removed, you will still have a rough barrel. Since you have already shot it, I would only polish it if you experience excessive copper fouling or you notice accuracy dropping off quickly. Some times it helps accuracy, but I think it is due to copper fouling quickly and dropping off the accuracy due to that , not a rough barrel. Just my 2 cents.