The ones I use are brass frankly I've never seen a brass barrel blow I've seen several modern steel ones go though. If you saw the post on the pistol I had that had the interchangeable nipple /flintlock conversion it has a brass barrel turned from solid stock I've fired that many times. Lots of old brass blunderbuss barrels out there. problem back in the day with brass is that much was cast and castings would be weak or have bubbles or be brittle brass. You wouldn't catch me casting one though
There are a lot of modern ML barrels made of material that the steel makers will tell you is unsuitable.
They used to make gun barrels, the export stuff especially, of very poor iron riddled with inclusions.
Some failed but most apparently did not. This was a problem at least into the second quarter of the 19th century and surely beyoud.
The problem is that a catastrophic failure of a gun barrel will virtually always hurt the shooter. A failure up the top flat or out toward the muzzle is the "safest". But if it bursts or fails at one of the bottom flats its anything from a trip to the doctor for wood shard removal to the loss of a hand.
But nobody wants to look at this side of the "lets use unsuitable material for gun barrels" discussion.
It does not matter to me is the slightest what anyone uses for gun barrels but people need to be aware of the risks in using unsuitable materials. I will not be around someone shooting a brass barreled gun or other such nonsense. I leave the vicinity.
I found out years ago what someones head looks like after being subjected to explosives I have no desire to see it again.
But hey, its America, people can do anything they want so long as they are willing to bear the consequences.
Dan