1. Not advised.
2. The .22 LR round will burst and unravel in a .22 magnum chamber nearly every time. It will fire a bullet downrange though and accuracy will be poor.
The gasses will exit the burst cartridge, usually harmlessly, though, and it it not advised as above.
However there are sleeves that can safely convert a .22 magnum chamber to use a .22 Long Rifle cartridge with no problems. The sleeve fits around the .22 LR cartridge.
What is the value of a Davis Derringer pistol magnum 2 shot?
No, they are different sizes.
There is no .25 Magnum. There IS a .22 magnum, made by Davis, and a .25 ACP. Value is about $50-$75.
10-140 USD depending on specifics
About $250.
The Butler 22 caliber single shot pistol was made by Derringer. The Derringer company was founded by Henry Derringer. Derringer pistols are the smallest handguns available and were most commonly used by women.
Magnums usually shoot faster. Hence the term Magnum
There are revolvers made with 2 cylinders that can switch back and forth between LR and Magnum ammo. However, those have a barrel bored to magnum specs. Simply adding a magnum cylinder to a 22 LR is not safe.
25-50 USD
No published data
10-60 usd
50 or so