I don't think I've seen this on here before, and it seems like it could be kind of fun, so here we go.
I was thinking about my collection, and a lot of my firearms are of older designs (some are actually old, some are replicas), I'm not necessarily talking about the age of the firearm, but the design for it (I.E., none of my 1911's were manufactured in 1911, and my 98k Mauser was not made in 1898). A lot of my favorite firearms, from those two examples from above, to my Peacemakers, and even my AR and AK which are both designs over 50 years old, have been around and doing their jobs for a long time. I think the firearms industry really is one where successful designs thrive, and over time it shows.
So, my firearm with the oldest design is a replica of a Colt 1851 Navy ball and cap revolver, not ideal for SD, but certainly fun to shoot. Who else has anything cool of older design that wants to share (look into it, you may be surprised how old some very popular designs are).