The problem that seems to occur is on the edges of some PE. Such as gun shields. Or where maybe some handling will wear off the primer/paint. I had one model that I built and painted- the AFV PAK 40, lowered to a second place in the local show because of this. I just didn't notice it and it cost a first. It's not so much about barrels, more about spots with small surface area where the paint may not have a good foot hold.
The picture below shows the edges I mean. Once the edge gets nicked it can tear and make a more obvious mark. The yellow arrows point to where I mean. The metal pointy bolts that hold the two shield parts together also seemed to get de-nuded with handling. (the shield in this example still has all the paint on it... if I find the motivation I may take one of the edges as they look now.)
