Toby, that's an unusual style of Purdey for one made as late as 1877. I have seen that type on Purdeys before as well. I have a Turner hammer gun with a small type grip safety which is probably of the type that Jim mentions. They were certainly around in the muzzle loading days as these are the guns I have seen most on. I would think my Turner is early to mid 1860's so an early centre fire breech loader. Lagopus.....