Because flattened primers are indicative of high pressure, anything that can increase pressure can be a factor. I'm not sure what the typical loads are for .270 gibbs, but I'm assuming that 40gr is a low load by the way you're talking about it. If that's the case, I'd assume that he's having a problem with his seating depth, either too long or too short. Between the two, too long is definitely more common among new reloaders.
This is because people will see the recommended seating depth in their reloading manual and seat their bullets to that specification without knowing what their rifle's actual max length is for that particular bullet. If you are exceeding your rifle's (not the book's) max length, upon chambering the round is being jammed into the lands of the rifling, and this can cause extreme pressure spikes even with a moderate load.
Conversely, seating a bullet too deep can compress the powder and cause pressure spikes if the powder is compressed too far.
I'm going to take a wild guess and say that if he were to chamber a round and then pull it out, the bullet would be scratched to hell.
Edited by HicksHunter (10/22/16 07:28 AM)