I once had a really nice 20Ga Hammer Double. This was some Lustrum(s) ago. Coach gun. Light, fast handling, good looking, I hated it. It beat me like a Rented Mule. This happened before I truly understood Scattergun Ammunition. With one or two exceptions, "Target" ammunition is NOT light ammunition. 12 or 20 doesn't matter. Target ammunition was developed and intended to break little clay birds at 30 to 40 yards. That is NOT light ammunition. 12Ga Light Target is NOT light with the exception of WW Featherlight. May years later I discovered Ficcochi "Trainer" in 20Ga. Soft. Mostly no discernible recoil. Effective for cowboy stuff. Shucked well. Just some thoughts.
There are right ways and wrong ways to Polish shotgun chambers. Shotgun chambers DO NOT need to be "open'd up." If you "funnel" the breach end of the barrel to make the double gun "faster" to load, you will have destroyed any value the gun ever had. Think lang and hard BEFORE you jump in there and destroy a shotgun. I posted before, 99% of hulls sticking in the chambers is because the shooter is using the WRONG ammunition. Wally World on special is not necessarily a bargain. Cheap doesn't equate to good. Be careful.