Mark,
For me hammer guns are endemic and have been so since the 1950,s. Not only have they been a joy to own and use,they have also proven over time to be a good investment.For your interest here is a case in point.
During the early 1960,s I was in the Carrs Lane,Birmingham shop of William Powell, talking hammer guns with Mr Powell,senior[Father Of Peter].At that time Powell,s had a Purdey 12G Pigeon hammer gun,with Whitworth steel Barrels on offer price 90 pounds!!!I vividly recall Mr Powell describing quality vintage hammer guns as ;"The most under valued antiques in the Britain today". How right he was. To day this gun would be worth 80-100 times the 1960,s asking price.

Roy Hebbes