My flintlocks have rust treated browned barrels...

The only stainless gun I own is a Ruger Mark II that I
bought in stainless as I put it in the boat to shoot water
moccosins...

My Knight Disc which is about 10-12 years old has a blued
barrel...It has no rust as I know how to keep my guns clean
and lubricated...

Any steel barrel will rust, if you are going to shoot muzzleloaders
it's best it you slow down and learn to properly clean and care for
your equipment...If you aren't the type to do so, might want to pass...