As often as not TOO MUCH choke constriction will cause patterns to
"blow" or open-up, i.e., sort of like a garden hose nozzle ... when you
go past the point of no return.
Did you pattern the "Full" choke that was supplied with the gun ?
At what distance are you doing your patterning ?
Good solid hold and a big enough sheet of paper to ensure you are getting the full shot pattern on the paper ?