I would say lengthening forcing cone(s) does indeed offer better patterns, both in central core density and in overall size of the pattern. 20 years or so ago, I sent the barrels of my field grade Citori off to Seminole Choke in Fla. I asked them to give my barrels their 5" extra long forcing cone treatment. Within a couple of weeks, my barrels came back with the shiny new forcing cones so long you really can't tell where the end. As this is my main duck gun and I mainly shoot 3" hard non toxic shot out of it, I didn't devote much time to paper patterning.
Bouyed by that success, I ordered a 20 ga forcing cone reamer and forcing cone hone from Brownells to try my hand on my inexpensive Savage 20 ga single shot. This reamer cuts cones 1.5" long. This gun I did paper test and the difference in core density was noticeable. I told my buddy about it and he asked me to lengthen the cone on his inexpensive single shot Savage. I paper patterned his before and after and it tightened the total size of the pattern enough that I went and bought a choke reamer to open his choke up a little. After that I lengthened the cone on my Savage bolt action 58D and my Mossberg 500 in 20 ga. In all instances, I had a better looking pattern and reduced perceived kick.
Then I bought a 12 ga reamer from Brownells and a hone and did the cones on my Iver Johnson Hercules. That gun is full and full and shot exclusively with Bismuth. In addition to more even looking patterns, the front trigger no longer bleeds my trigger finger when I shoot the back trigger.
While it is fun to read other's opinions, as one who has done this particular modification, I feel confident in stating that there is gain to be realized.
Mergus
