Rusting the bore is not caused by dry powder... rust will occur if the bore gets wet and has powder residue left in the bore.

Even then, and I am shooting T7 so there is a big difference in that and real BP or the Pyros, I shoot what i call a semi-fouled barrel, I never shoot a squeaky clean bore.

My ritual is just prior to the season I will take the rifle out and shoot it 3-5 times to check POI. It comes home I run a couple of windex patches and dry patches, the a very lightly oiled Xtreme patch... dry patch and load the gun up for hunting. It could stay that way for a couple of months before it gets shot.

The ONLY special care it gets is it never comes from a very cold temp to a warm temp. After a day of hunting in the cold it goes in the front seat of the pick-up which is cold and warms slowly on the ride home - then from the truck into the house. The next day the whole process is repeated... over and over again until such time as an animal of my choosing should decide to walk in front of the barrel.