Yes, you can break open the closed barrels. Yes you can break your weapon doing it. You will notice in the scrolling text window it will tell you the object condition. When the barrel reaches 0% it breaks open. If you are going to break open barrels use a weapon you do not mind losing if it breaks. Alternatively, you can use the fire dart spell, or demon oil to blow open the closed barrels. In one instance you must break a barrel to reach a path. Yes the barrel can contain items.
The thing is that some sealed barrels have randomly placed items and are usually empty. So be prepared to repeat the process a few times to maximize return.
ok, thank you for your replies. I may test that, but last time I tried, it was very slow to destroy the whole barrel. I think the open ones will be enough