IIRC, your rifle is referred to as an FN / Browning Trombone.
FN made some 150,000 of them from 1922 to 1974, which WAG would put yours as being made ca.1924-25.
In the condition seen in the pics, I would put it's value somewhere around $450USD, =/-.
If it were pristine, it would be worth almost twice as much.
The accuracy might be able to be restored with a careful (of muzzle damage), but thorough, barrel cleaning.
If that doesn't restore accuracy, I would take a hard/close look at the muzzle crown for cleaning rod wear or dings.
If it was shot with corrosive ammo, common in the 1920's, the bore might respond to a smoothing with JB Bore Paste.
You have a very nice family heirloom there.
Last edited by PetahW; September 20, 2012 at 08:57 AM.