My personal experience is, I had a Model 21-1 made for me with a set of 30" 20 gauge and twenty eight gauge barrels.
I did ok shooting the 28 gauge set but could not hit the broad side of a barn with the 20's.
Traded it on my Boss and was a happy day for me.
I had heard of issues with barrel regulation on these CSMC 21's.
When I ordered I discussed this with CSMC.
Beautiful gun. Would I get another? Yeah probably, but would send off to verify barrel regulation.

Mike Proctor