From my measurements, most seem to have a 2 inch or less taper, and few have much if any parallel. Exceptions have been a Winchester Heavy Duck Model 12 that had 4" taper and a Belgian guild gun I just got in to open the chokes, where the taper was 6" long. Don't know what kind of patterns it threw before alteration as I didn't have time to shoot it before modifications were made. Just my experiences. MkII