I just thought I'd share an observation that I've had recently. That being that Korean dips are a perfect warm up for me before doing dislocates.
I've been struggling with a bit with underhand dislocates, and I've tried various approaches and warm ups. But working a set of Korean dips as warm up has had quite a dramatic effect. I'd say that I easily got an extra hand's width more narrow on both sides on over and under dislocates.
This is particularly noteworthy for my underhand dislocates which have been a bit stalled recently. Not only did I easily get a way more narrow grip than I ever have, but it completely removed all the discomfort I've had in my left arm.
This should of course be worked as a warm up only if you're already comfortable with Korean dips. But if you're feeling stuck, try giving this a shot.