Two guns with double under bolts, that feature a lever hold open. An Italian Prandelli and Gasperini and a Spanish Ugartechea:

[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]
[Linked Image from i.ibb.co]

The reason becomes clear with a quick examination. Both guns have hidden third fasteners that have to be held out of the way when you go to close them, just as Dustin pointed out. Not common.The Italian gun has a hidden round bolt, operated by the top lever, and the Spanish gun has a very well fitted “Purdey nose” on the breech face.

For what it is worth, both are 3” guns wearing European magnum proof. Not sure why they thought they needed a third bolt, but, that might have something to do with it.

Best,
Ted