I think, in most cases, the name of the steel used in the construction of barrels does not mean that the steel works in question actually produced the barrels. The Verney-Carron catalog from 1922 refers to "the principal qualities of steel THAT WE USE THIS YEAR IN THE MANUFACTURE OF OUR GUN BARRELS". In specific, they mention Jacob Holtzer steel, but I think the above sentence makes it clear that V-C and not Jacob Holtzer actually makes the barrels.