New Bores
Clean the bore of each new firearm before using it. Manufacturers often treat the inside of the barrel with a combination of grease and oil to prevent rusting as it sits on the shelf waiting to be bought.
Fouled Barrel
Copper and lead are the two primary culprits of a fouled barrel, depending upon the bullets of choice. Specialized chemical cleaners will remove both, but they have to be used on a regular basis.
Rust Protection
A newly cleaned barrel bore has no protection against rust. Running a slightly dampened oil patch through the bore as a final step in cleanup ensures that rust cannot gain a foothold. Run a quick, clean patch through the barrel again before firing.
Proper Equipment
The proper equipment makes treating and cleaning a bore easier. Use barbershop jags in the correct size and cotton swabs large enough to cover the bore but still fit though easily. One-piece cleaning rods are less likely to break when forcing down a close-fitting bore.