Just sold a derringer 25 Davis for $75
About $150
$75
50 USD
It is not adjustable.
The maker of your Derringer is no longer in business. Sorry-
25-100 or so
Davis Industries is closed. Same gun is made by Cobra. Follow the link below to an owners manual.
Leave this to a trained gunsmith.
25-65 USD or so
50-150 USD depending on condition, papers, box, etc..
This would be a Davis Arms .22 Caliber Derringer.