I have no idea the make/model. I was just asked to incorporate one- I worked from photos. It's my understanding they had a guy back east make the hero axe- it may be the same mech I linked to above. I know they said they were going to use a real mechanism.
As far as the hammer being used as a latch to keep the axe head closed- in the "movie world" that may have been the case, but the prop didn't function that way. The axe head just slides back and forth to cover it.
One of the concepts I did had the trigger/hammer assy pop down out from the reciever as the axe head came back. The head of the axe also rotated slightly at the end of it's travel to sit at an angle- but obviously they didn't go that way. I like the way it ended up, it looks period and even plausible.
I remember when they ran down this job for me I thought it was one of the most ridiculous things I'd ever heard- but seeing it in action, it ends up being pretty cool.