Back when I managed to paint my XD9 shut, I made a visit to the gun smith that has been so helpful to me in this journey. He forced the slide open and showed me the hand position that he found gave him the most leverage to do that. He was kind enough to let me take photos of that hand position on a future visit when I wasn’t in such a flustered state.
Here are the two views of his hands on one of the guns from the shop:
I’m not going to tell you when it’s best to force the slide versus taking a problem gun to a qualified gunsmith, but if I ever paint another gun shut (no plans at this time!!!) I’ll have a plan for getting the snap caps out.