get some finger cots (large size) in the pharmacy section of your local wal mart. After you load the rifle, just roll one of them over the muzzle. This will keep all the water out of there and you can shoot right through it. The breech end of the rifle, I do not think you really have much concern.

At the end of the day remove that muzzle cot, and with some oil on a rag, wipe the barrel off real well. Then you have no worry of rusting.