mpr pict/shack is running a promo that seems to block access to your pics. So, without checking proofmarks there ain't much I can say. There was a Manton shop in London around the time your gun was made. They sold Birmingham guns of good quality. According the only book I have that notes this shop the gun should have the London address of 6 Dover St on the rib. Of course the book can be wrong so you should check that the proof marks are from Birmingham. You can do this on-line.
If the gun is Brit it should date from the mid 1870s to 80s. It appears from the tiny picture to be in banged up shape. Is it?
