Here in Florida on a hot summer day (95-98 f) I have to be careful when shooting Winchester factory ammo from my Savage 7mm Rem Mag. It only seems to happen with the 150 gr. Power Points, but my primers are really flattened and there is evidence of severe case stretch in front of the belt. This never happens in cooler weather and is less noticable with other ammo. I have never checked headspace in this rifle, but that could be a contributing factor.