nitride is no where close to ceracoat. The nitride process involves putting the part (barrel) in a molten salt bath. Every bit of exposed surface is treated, barrel bore included. No dimensional changes occur.
Ceracoat alters the dimensions, it has some significant thickness and can't go in the bore. It's basically a paint job for cosmetics.
I offer nitriding barrels, but that Dynatec stuff contaminates the salt bath and therefore they will not do them.
Modern Spartan Systems just came out with a coating that they say is more durable than ceracoat. It does not require heating to cure. It is called DutyKote.
https://dutykote.com/