The forcing cone needs to be 2.5" long for the typical person to notice. Anything less and they think they got ripped off. Whether it does anything to improve patterns is a big question mark. I have seen a noticeable decrease in fliers when using buffered lead shot of #2 and larger with maybe a perceived evenness in shot distribution in patterns with smaller shot- maybe (repeated intentionally).
I've read mixed reports with longer forcing cones helping to prevent occasional pressure spikes with the larger sizes of steel shot. This seem so of be a phenomena like detonation in metallic cartridges, some believe it happens but it is difficult to repeat in the lab. I lean toward longer forcing cones helping as it can't hurt if enough steel is left in the barrel.
I haven't seen any change in recoil when forcing cones were lengthened and can't see how that could even be possible unless the velocity was somehow changed. Shot charge weight would remain the same and what little metal would be removed should have negligee affect on gun weight. It might have some change in the recoil curve but that is something that is determined per individual, gun, and load rather than a blanket statement.
