Toby,my gun has two dogs protruding from the front of the bar,which are the ends of the mainsprings. They insert into channels in the forend. There are two "rocking spring tensioners" and you can see in my picture the small lug,attached to the barrels flats,coming down on the tensioners. The gun pops open when the top lever is pushed,and,it seems to me, That the springs,while bent under the pressure of the open barrels act as an assist in closing the gun up. What's not to love.
Judging from the picture of patent #425,I've seen this is what the gun ius built on.
So,what's up with that?