The metals used in the braze will not have the same qualities as the original barrel steel and is the weak link in the chain.
How much trust would you put into it when there are a few tons per square inch pressure subjected to it every time the barrel is fired.
If I'm honest, it upsets me every time I see a lovely pair of Damascus barrels that are past their best and have to be scrapped but the truth is, when they're finished, they're finished.

Rust never sleeps !