I think that what you have is a hammerless gun with hammers. By that I mean that the gun appears to cock on opening as indicated by the cocking dogs on the knuckle of the action. The hammers then just become cocking indicators but can probably be used for de-cocking the action. The safety catch is not something usually associated with pure hammer guns. During this transitional period between hammer and hammerless actions coming in there were quite often features such as these as people were suspicious of a gun that could not be shown to be cocked or un-cocked. Unusual and interesting gun all the same. Note that it only proofed for black powder. It appears to possibly be pre 1875 with the proof marks. Lagopus.....