They went by many names and were made by a number of firms. It's most commonly known as a "British Bulldog" or a copy thereof. The originator was Webly & Scott with "The British Bulldog", but with it's popularity so came a number of imitators. Either .455 or .44 calibre. It might say as much on the top of the barrel if one where to look. They were cheap, robust and powerful in their day. (late 1800's to early 20th century). Frequently found made in Belgium, England and France.