this is a topic for which a search on this board will give you days worth of reading material
it seems that they have become what I shoot most of the time lately,
the readers digest version - damascus and twist barrels in proper condition (good wall thickness and no or light pitting) are generally considered safe to shoot with proper loads by most of us
NOW- ask what a proper load is
I do prefer lower pressure loads - no matter what the barrel material - they are old guns with old wood