[Shane I Reed]

So my local shop has some old Parkers. He told me he has 3 more what he calls "parts guns" that are in shootable condition. He just got this one in but the rest are where he has a work shop for gunsmithing. I am going to try and save them all. I am starting with this 1877 12 guage? basket case. I have never worked on guns before but willing to put time and effort in to this new passion. The gun is very dirty like it's been hanging in a hunting camp for years. I believe someone painted barrels black. Mechanics actually work! I am going to be looking for a part that goes on barrel which catches to latch. Part of that broke off and so my question is, where the heck do I start on this thing? Cleaning off my former archery work bench to tackle project. Also, where can I find a guide to markings so I know exactly what I have?