You cannot "overclean your gun".
Think of it this way.A shooter can take his shotgun to the range and fire 50+slugs throughthe barrel. Keep in mind that these slugs are hunks of lead (sometimes with a copper jacket)being propelled by gun powder (which causes extreme heat and pressure inside the barrel) typical shotgun slugs travel at about 1500-1700 ft. per second and some of todays modern sabots are flying around 2000 ft. per second or faster.

So, to sum up overcleaning. Running a brush and some oil down your barrel will not damage your shotgun at all. (I dont care how fast you scrub it)

The only issue I would say to be aware of is not to leave EXTREME excess of oil inside the barrel. Make sure you wipe down the insides of your barrel with a dry cloth after you brush your barrel and apply your solvents/ oils or both.
Also,there is no "break in" period for a "smoothbore" shot gun. (BECAUSE ITS SMOOTHBORE)Some guys like to "break in" or "season" thier barrels which canaid in better accuracy out of rifles, muzzleloaders or shotguns with"RIFLED" barrels.

Believe it or not, sometimes when a rifle or shotgun with a rifled barrel comes from the factory, There are still some imperfections left over from the rifling process. I have purchased guns (brand new) that still have had metal shavings inside the rifling that effected the way the firearm performed. Over time, with proper shooting and cleaning procedure, These firearms became extremely accurate. They just needed the lands and the grooves of the riflingto be cleaned out and seasoned over time.( HOWEVER, A SMOOTHBORE SHOULD BE READY TO SHOOT RIGHT OUT OF THE BOX) " with the right ammo. The mechanics inside a smoothbore are simple. If the diameter of the inside of the barrel is correct for the size of the slug itwill be shooting and there are no obstructions or foriegn debris inside the barrel.....you should be all set.

However, with your smoothbore, if you are getting patterns that are all over the paper at 50 yds. You better check your scope (if you have one) If you dont have a scope and you are still getting slugs flying in every direction @ 50yds or less.....ODDS ARE ---IT IS THE SHOOTER (not the gun). You should also experiment with different brands of slugs. Certain slugs fire better out of certain shotguns. Either way, you should find some brand of slugs that will shoot atleast 4 inch groups. If you are shooting 18 inch groups (and you dont have a scope that is loose or a scope at all for the matter).....it isnt the gun, it isnt the slugs,......it is the shooter.

good luck andI hope this has answered some things for you.