Bisley S7 issue

Shoots like crazy. Extracts poorly on 2 chambers, even with reduced loads. Not being super knowledgeable, and not having had this issue with any other revolver. What would most likely be the cause. Also have to trim the brass a fair amount after each loading. Both Starline and Fed. Thanks for the input.

Could be something as simple as a rough chamber. When I've had this kind of issue I run a bore mop covered in JB Bore Paste through the chambers with a drill press. Always seemed to clear it up for me.