What shotgun you're shooting has little, if anything, to do with it ...except maybe barrel length ....but most any modern shotshell...completely burns its powder well within the first 15" of barrel length or so...based on what I've read.
Some powders just seem to leave a lot of unburnt powder behind...like Hodgdon Universal in a 20ga ...standard 7/8 oz load at 1200 fps ( I load about 15.5gr ) in that load...but Universal is a little slower than some and for that volume of powder its a little dirtier than most....but in a 28ga - Hodgdon Universal is relatively clean...and I load 13.8gr...in that recipe...behind 3/4oz at 1200 fps...( not a huge difference - but in the 28ga, it seems to burn more completely )....