When I was building my double rifles, I used a drop lock very similar to the Perazzi. I fact, for my prototype I used a modified Perazzi assembly.

For my "production" guns I used coil springs instead of the "V".

By the way, the one that I'm making now will be a side lock with back action coils springs and interceptor sears. In a .700 NE doubling is not an option.