I hope Bolek comments here, from the pictures it looks like when you pull the dog back to prime the pan it sets the lock ready to fire. Lower the dog with the pyrite over the pan cover and the gun is ready to fire. Edit: It figures I got it wrong. In the video below this post it is set by pulling the dog towards the pan. It's art in motion. Thanks Acer!
I miss Bolek posting on his builds here. He was a very good instructor on the subject of wheel locks and their construction.