Ive cut down a .30 and .25 barrel to 500mm and still shoots very well. You'll have to make a leade somehow i used the lapping compund and brass screw trick and worked well for me. If you had a reamer and lathe obviously would be best to make a proper leade.
If you make two barrels it is likely that the one without the choke will be fairly pellet fussy. It can still be accurate and will likely shoot some slugs good as well.
If you make two barrels it is likely that the one without the choke will be fairly pellet fussy. It can still be accurate and will likely shoot some slugs good as well.