The grain does run lengthwise in a barrel. The barrel has the greatest strength that way. However, when forging wrought iron, it is usual to make your bend across the grain as opposed to with it. When I say "across", I mean perpendicular to the grain. If you made the bend along, or parallel to, the grain, it tends to crack along the grain. That is why your make sure the grain is running through the spur and bottom jaw when you forge a cock. Otherwise, the lower jaw would tend to snap off along the grain lines. If you need to forge a bend along the grain as in a barrel, you need to make sure you keep the metal hot, as in bright orange or yellow, while you are working it. When wrought iron goes to plain red, it needs to go back in the fire. For hammering wrought iron into a die, it needs to come out of the fire white hot, almost at welding temp, so that it flows without creating cracks along the grain. There are similar problem working tool steel, but since you didn't ask about that, I won't go into it.
As to being able to see the grain, I have never noticed it in antique barrels, and you don't normally see it in my wrought iron mounts or lock parts. You would have to etch the metal to see that unless it was really crude stuff. For barrels, you use the finest grain iron you can get. I have some very nice third run stuff I am saving for barrels. In the old days, in England, they preferred to use recycled nails for barrels and locks. That way, you can be sure the iron had been worked a lot before it was worked into barrels or lock parts.
Did you know that iron is the most recycled metal. The same iron has been used over and over again for centuries. To some extent, you can say the same for cooper, silver, and gold. Just an interesting thought.
