It is a rifle - the levels of various technology in GD are anachronistic to real-world technology of a similar time period. In some areas GD is more advanced, while in other’s it is more primitive.
These barriers cannot be destroyed, as that would defeat their primary purpose, which is to create alternate paths through levels. We do have other things that can be destroyed to gain access to “hidden” areas. Like there are sometimes places in the fieldstone wall where it is crumbling and you can blast your way through.