[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]

The barrel lug locks into this trigger guard/underlever. This also cocks the hammer. My other break action uses a striker that is pushed back by the lever and locks on the sear.
It looks like it was originally centerfire. Gauge marks are 29/43 but the the left of 2 is bad pitting so it could of been 129.

Im sorry for peicemealing pictures. Im splitting time between work and caring for our toddler