ORIGINAL: eldeguello
You are correct that straight-side, sharp-shouldered cases need little, if any, trimming. The brass doesn't flow much. But rounds like the 300 H&H are just the opposite. Even the 270 Win. stretches pretty badly...
Yep.....The 300 H&H is the prime example of why a belt was needed. Not enough shoulder angle along with a relatively sharp body taper to headspace on properly....In effect, causes brass to flow forward much faster.