I haven't heard of this phenomena with the M-14. I served with many Vietnam vets and have heard similar stories about the M-16 when it was first introduced. It was notorious for jamming and caused the death of many US soldiers.

This article, which was written in the 1980's, goes into quite a bit of detail about the many problems surrounding the M-16 rifle that led to it's initial poor performance. It discusses issues associated with the design, introduction, acceptance and roll out, as well as the bureaucratic nightmare that encompassed it all.