I have limited experience with this but recently did the forcing cones in a double to improve the patterns. When I reamed the cones I took notice that the chambers were quite tight, almost cutting a completely new one and then lengthened the cones out to 1.5" from .5". When tested the patterns only slightly improved (less than 5%). What I did notice was a reduction in recoil, which some claim that forcing cone work helps and others say it does nothing for recoil. In this case it did. I would do this modification again, it was cheap and easy and made the gun more pleasureable to shoot.