Dear Jeremy The BUN nut is a feature of Bakers series locks considered a stronger plan . as is the greater length between the 'side nail' holes this was to lessen the possible damage from the breach plus hitting the rear side nail (Bolt some call it ) but Potts wouldn't. If you file a central slot in a common screw driver it will fit the male screw (Tumbler Pin he would call it me too) Sounds like you have similar percussion guns ? . The stocking is so unusual its anyone's guess what it might have been intended to have poor boy shimmel so whatever you fancy or have to hand would do .While the lock will work fine its miles away in from any US style . Just under 6" would be carbine or Fusil maybe Baker rifle but Commercial so any ones guess if their should be a detent that would be a rifle, but it all depended on what the customer asked for. Hope that helps . Rudyard
PS it occerrs to me that the extreme croodaty of the stock finishing could be deliberate the setting of the lock & the two rod pipes ( The rear one allways a pain to inlett !.) Suggests the stocker didn't lack skill. Definatly an odd ball my guess then is its for Chunk gunners they like such an unusual stance one famous chunk gun had the forging scales left on the barrel deliberatly so. They like a sort of deliberate' reverse vanity ' as I call it . long heavy barrel that fits suggest you try "Is this a chunk gun?' post they are a tight group good fun group one might regognise it The proportions & lock aprons suggest the maker was more capable . Rudyard