If it's a Flues, take the bbls off and look straight down into the action from the top of the breech.
You should see the locking bolt just sticking out if the lever is returned to the center.
Pull the lever over as if opening the gun and just below it you should see a semi-circular disc.
Actually you can see the 'disc' even with the bolt forward.
That semi circular thing is the barrel latch.
The barrel lug hits that upon closing to release the lever from the 'locked to the right' open position.
It is supposed to be spring loaded (small coil spring) so it pops upwards slightly and locks the bolt and the top lever open when the bbls are dropped open.
If the barrel latch is there,,it may be only the small generic coil spring missing. Or it could be there but gummed up or rusted in place and not doing it's job.
Push down on it with a small screwdriver and see if it has spring tension movement up and down. It won't be alot,,perhaps a 1/16",,maybe a little more (so scientific).
Sometimes the small notch in the underside of the bolt itself that it snaps into is worn and it doesn't catch securely to hold things open.
Takeing the bottom plate (trigger plate) off will reveal alot.
The bbl catch and spring if they are there drop right out w/ the bottom plate off. You can also inspect the notch in the bolt, clean it out, lube, ect. But removing the bolt itself to repair it if needed/worn is more involved.
