What kind of condition is the crown of the muzzle in? Over time and lots of usage, the crown can wear down, a bit and accuracy can fall off. A simple re crowning of the muzzle, or in bad cases, shortening the barrel and 1/8 or 1/4" and then re-crowning the muzzle will usually return an old barrel to top accuracy.
Also put a length of brass rod down the barrel, after the bore is oiled, and then seat an oversized lead ball( bare) in the barrel( ie. use a .36 cal. ball in that .32 cal. barrel). Once the over sized ball begins to travel down the bore freely, upend the barrel and shake it up and down to use the brass rod to knock the lead ball out.
Now, use calipers, or a micrometer to measure the grooves and lands as they are pressed on that over-sized ball. This will tell you if there has been any significant wearing of the lands over the year. If the land-to-land( bore) diameter has increased significantly, you may want to invest in a slightly larger ball mold, or at the very least, use a thicker patch with your existing balls.
It is not uncommon with any diameter RB gun barrel for there to be enough wear on the lands over time, that you need to increase the thickness of your patch. If you frequently recover spent patches fire from that- or any rifle-- the patches will TELL YOU when anything is changing in your barrel( including any wearing of the crown). :hmm: :hatsoff: