Naemanson: DAve is right about the estimate being very low. From the way you describe the rifle and its rarity even his estimate may be low. I'm not familiar with the Lancaster but in general the questions to ask are: Does it fire safely? are the original box and tools with it? Any Pitting in the barrel or damage to the blueing? How many were made? If over say twenty thousand, your father's rifle would command a higher price. I suggest in addition, you check with the Smithsonian Institute, or the British hunt clubs for experts on the weapon as I assume given the quality of the rifle that it was made for someone with money. It would have been out of the reach of the ordinary hunter or estate game keeper. Even in the U.S. the rifle would have been a rich man's toy. If you know where he got it and could trace the oringianl owner, who can affect the price as much as what. Say for example, if the gun was owned by U.S. Grant or George Custer it would be worth more than say if it was owned by the local mayor of Bangor in 1855. Kindest reguards, Neil PS keep us posted on how it goes.