I had the opportunity to open the choke on the left barrel of a Browning BSS 12 gauge with a non-slective trigger. My friend wanted both barrels to be choked the same for shooting sporting clays. Both bores measured right at .729" - .730". The right barrel had .015" of choke with the taper starting approximately 3" back from the muzzle. The left barrel had .031" of choke with a little more than 4" of taper. That is the longest taper I've measured in my very limited experience opeing chokes on mostly European guns. The 4" of taper actually limited the choke reamer bushings movement towards the muzzle so the reamer only partially exited - maybe only about 1/2 the reamer was out of the muzzle when through reaming. But it didn't seem to cause any problems. I got the choke opened to .016" of choke. I left a little for polishing but the steel cut so cleanly it polished very quickly and easily.
We were both curious how the left barrel would pattern with the longer taper. In an unscientific check both patterns appeared to be almost exactly the same. And both barrels shot to the same point of impact and were centered up well. But the patterns weren't divided in to quadrants and pellets counted. It didn't appear that 4" of taper made any difference in the pattern when compared to the right barrel with 3" of taper.
