Here is what I found-all that that unnecessary loopcuts were causing the issue. It is probably because you used mirror modifiers to make the barrel. *Mirror modifier just make a duplicate of the mesh and mirrors it. It does not merge the vertices to the original mesh.* 

In your case the easiest way to solve it is by selecting all those edges (which you have beveled) except any one among them by <kbd> alt</kbd>+<kbd>shift</kbd> + **RMB** and then delete them by pressing <kbd>X</kbd>.**Dont forget to switch off all the modidifiers except *curve modifier* before selecting**
[![enter image description here][1]][1]
[![enter image description here][2]][2]
[![enter image description here][3]][3](Select the edge and press <kbd>G</kbd>twice tp slide the edge)
Which will get u this:
[![enter image description here][4]][4]
To solve it in the proper way, you can apply the mirror modifier and box select the vertices and merge them with <kbd> alt</kbd><kbd>M</kbd> > **merge at center** .(You wont even see the vertices cuz they are too close to each other).It is a tedious job.


  [1]: https://i.sstatic.net/ucF28.png
  [2]: https://i.sstatic.net/W4CWR.png
  [3]: https://i.sstatic.net/XBuQ0.png
  [4]: https://i.sstatic.net/ImHSk.png