That kind of fold usually comes in when using (way) too much lube - the lube getting trapped at the shoulder, and nowhere to go to. After each pass, you need to respread the lube on the case to avoid 'pooling', which will help you avoid such events.
FWIW, if you need to use a cheater bar on a Rock Chucker, you're doing something wrong - 1st thing coming to mind is annealing too light/not far enough down - one or both. The other is not enough lube, but seeing the case with the shoulder fold, I doubt that is the issue.
Rick, shooting these Martini's is kinda addictive - and there's no cure! It's actually the challenge of getting them to perform in spite of all the 'issues' these rifles have, that makes it interesting. She's not really forgiving, and will bite you if you hold her wrong, but if you handle her with respect and know her quirks, she'll oblige by performing quite well.