In answer to your question as to how long they will last . It will depend on how much they have been used ,abused and maintained .They are not guns for heavy continuous shooting ,game guns as opposed to clay guns .Guns of this sort were made with the idea of light loads [1oz].Lancasters and Grant 12/20's were a stronger action than say a Turner "Featherlight" or guns produced by the likes of Palmer Jones and Hellis for example .Like the 2" guns they were cut to a minimum ,barrel walls struck down to .025" actions lightened as much as was dared and stocks hollowed out .
