Ah OK - yes, it might be. Completely depends on the barrel that you're modelling. On the example one I linked above for you the hexagon part was welded on, and there was a cylindrical cap. :)
Show the high poly asset? What was the error/unnecessary feature that you needed to paint out? The bake you have looks fine; it's captured all of the detail I'd imagine as expected. No errors on the screenshots? However, don't be afraid to use more geometry too. We're in 2015, and modern GPUs (especially for AAA games) can…