You only need to worry about damaging the crown if you drag the cleaning rod against the muzzle enough to wear it; no easy feat with an aluminum or brass cleaning rod.
With large calibers, it is simple to keep the cleaning rod centered, thus the remote possibility of crown damage is eliminated.
Use an agressive solvent (Shooter's Choice, Accubore, etc.); put some in the bbl. with a nylon brush after you finish shooting, if you can. When you get home, use some more solvent. I usually let the revolver or pistol sit overnight and run another patch with solvent on it through the bore, then use dry patches, and finally some sort of rust preventive (Shooter's Choice Rust Prevent, Tuf-Glide, etc.).
This method will usually remove gilding metal fouling. For tough leading, I have found that Lead Away cloth, cut into patches, works just fine. Use a patch of Lead Away over a couple of plain patches, so that the fit is very tight. Use solvent on the patches as well. Run the patches through the bore a few dozen times. Repeat until lead is gone. Clean bore with cotton patch/solvent, then coat with rust preventive.
Sentry Solutions (Tuf-Cloth, Tuf-Glide, etc.) has a new product, Smooth-Kote; it is a blend of lubricants, including MoS2, in an isopropanol carrier. You apply it to the clean, degreased bore, and the MoS2 plates the bore so that lead or gilding metal don't stick. I have used it for a short while, and it appears to work well. It is like using MoS2 coated bullets, except you just treat the bore, not the bullets. For a little over $30, you can get an Armorer's Kit from Discount Knives. It has a complete array of Sentry Products, including a Tuf-Cloth, Tuf-Glide lube, Smooth Kote, a synthetic grease, even rubber gloves and applicating tools! Here is the URL:
http://www.discountknives.com/ click on 'accessories,' then 'Tuf-Cloth.'
Hope this helps, Walt