Your UV islands may be too close to gether. Give them a mit more elbow space…
Also try a less cluttered mapping. Just unwrap the barrel sides as one cylinder with one vertical seam.
If that would interfere with your intended texturing, add a second channel and work with that.
@KVogler
I gave the UV Islands more space between each other and also tried several other UV-Layouts, sadly there wasn’t any difference.
@Tim Hobson
Neither Edges or Faces as smoothing groups makes a difference. How much increased does the lightmap to be ? At the moment it is 1024.
I tried different UV-Layouts.
@rimau
Hopefully I did it right, but marking the edges as sharp did’nt make a difference.
random question, when you imported it did you use “compute normals” or “import normals” in the settings?, using import normals can mess up smoothing like that even if you set the smoothing groups properly in blender.
also if you want you could upload it and we could take a look at it.
size matters, in the blender screen shot i can see the grid , to me that says theres a good chance your using the default size for working, remember that 1 blender unit equals 1 unreal unit , the normal size of the barrel should be around 100 units high
the uv layout needs a lot of work imho, you need to reduce the ammount of seams, a simple barrel like that only needs 3 seams to get a decent uv layout.
hopefully the pic will show what i mean