Gary
check the proof marks - British or Belgium?
a quick search with BING showed several hits for
"gun Renkin Brothers" including
http://www.thehighroad.org/archive/i.../t-500093.html
There were so many makers that did not survive - every muzzleloading gun (IMHO) needs to be evaluated on its own,
I looked at what seems to be a high quality 15 bore cap lock a week ago- no name, early Birmingham proof marks, "London Twist" barrels ( but don't they all), but no name on the locks or rib. BUT platinum blow out plug, decent engraving, and nice stock work on a great piece of walnut. so - no name junk - or quality piece?? Still thinking on that one.
PS-
forgot to check my favorite Belgium gun site
http://www.littlegun.be/arme%20belge...belge%20gb.htm or
http://www.littlegun.be/
they list Rankin - show some examples and have a picture in the portraits link
http://www.littlegun.be/arme%20belge...enkin%20gb.htm