Matt, fantastic questions and I hope I can answer this in everyones opinion but I'm sure I will not be able. I can only answer to my findings with my 20 gauge that I shoot now. As I test shells I notice a drop in every shot for about 6 shells ran through the gun. As most very I would be safe to say that I lose about 2- 3 % a shot for 4 - 5 shot after losing up to 10% in about 6 shots.

I do give my gun a real good cleaning after 6-8 shells shots.

When I take the gun back to the cleaning room I will spend a good 1/2 - 3/4 of anhour starting with a wrap of 00# steal wool on a cleaning brush,in the drill andrun it up and down the barrel a few times. I will change and run a white cleaning patch to collect the crud and then drop down to 000# steal wool do the same. I use WD-40 everytime I changethe cleaning rodand then after I finish with the steal wool I go to Red scotchbrite, blue, green and end up using white for the last of the cleaning until I can run it up and down the barrel and it comes out White with no dark or black fowl at all on it.

When you look at the inside of the barrel at a light it should reflect light all the way down with a glass finish. It is easy to keep this up and just as easy if it don't work for your setup to get it dirty once again.

Every gun I have cleaned for friends this way has shot much better then it did when it was dirty, the only difference is spending the time working on your barrel...