The easiest solution would be to put an adjustible rear sight on it to get the pattern where you want it. There's 2 or 3 brands out there that fit the 835. The forcing is the first step down in size on a shotgun barrel, just in front of the chamber, with the next step down being at the choke. In the case of an 835 it is backbored which I think means that it has only one step down and that's at the choke. Which also means that it needs to shoot a more open choke that a regular barrel. Some of the other guys here might have a better explanation of forcing cones though.