A break cylinder hone works just fine - check your work often - and do the improved cylinder bore. IT won't take long to open up .009" or so to .001 or .002" of choke which will be as none - maybe 20 minutes. Use a variable speed electric drill- it's easy. Ct for a min or so, then measure. Go sowly and measure often.
: I've done this to many shotguns, 10, 12 and 20 bore, in changing their chokes to improve patterning with specific loads. The easiest way to remove the chokes compleetely, is to cut the barrels off and replace the bead, however to save one choked tube, save the modified one, and ream or grind the little amount of imp/cyl choke from the other.
NOTE!! ; 1st of all - shoot the imp/cyl barrel with patched round ball first. Glue a small piece of knotched wood to the breech for a rudimentary sight for better aiming. IT makes a BIG difference. If the accuracy isn't good enough, then remove the choke slightly, and re-shoot. Stop when the barrel gives the best accuracy, or when it's a true cylinder - whichever comes first. It's easy, it's simple- all you need is an electric drill & something like WD40 as a honing oil. I used to glue emery pathces to the worn out stones with cyanoacrylate glue (CA) and that worked even better than just the stones.
Daryl