I suppose if you had a NFA M14 and fired mag after mag full auto the receiver would reach temps high enough to be a problem, but you would not be able to see through the scope for all the heat coming of the barrel.
You are probably right as my experience is with the M14s and M25s while in the service. The Al mounts were a big no-no as told by our gunsmiths. We used Brookfield steel mounts w/out any issues.
Said that, the iron sights are great!