H&R began manfacture of single-shot, break-open shotguns in 1908. These were chambered in various guages and several barrel lengths and chokes. There is little collector interest in these guns.
These break down into three pieces rather easily. These are: Stock (the wooden part that fits against your shoulder while firing), Barrel (the long tube), and the forearm (wooden part that fits under barrel and is supported by non-firing hand).
Below are some links to parts suppliers with some exploded views;
Hope that helps some