Why do vertices move when 'Smooth Vertex' is applied to mesh? I'm having a problem when my meshes exported (to FBX) whereby Blender will smooth the model down.
To replicate the same problem I used Smooth Vertex and as you can see from the before and after the verteces on the barrel have moved. When I import the mesh into UE4 the problem is a lot worse with segments of the mesh completely missing. Its probably down to a fault of my own but this is my first ever modelling project so I'm still learning.


UE4 also displayed this warning message when I imported the FBX mesh.

Warning: No smoothing group information was found in this FBX scene.  Please make sure to enable the 'Export Smoothing Groups' option in the FBX Exporter plug-in before exporting the file.  Even for tools that don't support smoothing groups, the FBX Exporter will generate appropriate smoothing data at export-time so that correct vertex normals can be inferred while importing.

Any ideas as to why this may be happening would be greatly appreciated.
when exporting to FBX, Blender looks at the Modifier Stack of each object and applies the RENDER modifiers to the object. I can only guess without checking the file, but I suspect that you have a SubSurf modifier on your geometry.

Uncheck the Render Visibility (red arrow is pointing at it in the screenshot) and export again, it should be fine then.