You are absolutely 100% correct with your assessment!Dave,
I'm guessing that wasn't done on purpose.
I've heard stories of that happening as well. The case from the .308 in a .270 looked similar, except for the case separation and mushroomed head from the pressure needed to size a .308" diameter bullet down to .277" diameter.I did have occasion to witness the puzzlement of a fellow with a borrowed hunting rifle looking at his missed target and then quizically at the extracted .308 case. It lacked a shoulder and sported a .40+ caliber mouth. "Is it s'posed to look like that," he asked? The in-law who'd loaned him the rifle had told him it was .308. I had the pleasure of introducing this good fellow to the science of reading barrel stampings. In this case, the stamping argued more in favor of 30-06.