This one tool.
http://www.woodcraft.com/Product/2...ep-V-Parting-Tool-3-mm-Intermediate-Size.aspx
Virtually all incise carving of the normal longrifle variety can be done using this one tool, and I believe that most, if not all, incise carving found on 18th-19th century guns was carved with similar tools. (I use it to outline all my carving now, incised and raised... and the raised carving with incised "edges" which is commonly seen on Lehigh and Lancaster guns.)
It can be chased with a mallet if you wish. Basically, you are engraving wood. I push mine with my hand....CAREFULLY. It can get away from you with a simple push. Usually, I will give it a little "wriggle" as I gently push it. The "wriggle" doesn't show in the carving, it cuts cleanly with more control than just pushing. For the tightest curves I used to have to chase it with a mallet, but I now can push it all the way around. One tool. No fuss, no muss.
Assuming you have the proper coordination and artistic talent, once you get the hang of it, incising this way is fairly easy. There is, however virtually NO room for error. Follow your pencil line precisely, don't let it slip!!! With relief carving, a lumpy line can be smoothed out somewhat. Not so much with an incise line. Once it's there, it's there. It can be smoothed SLIGHTLY (too much, and you make the line too wide) with either the V tool or a handy, dandy checkering cutter (which is basically a small V shaped file mounted on a handle).
Other than properly shaped small gouges to make the little "chip cuts", and a gouge or two to make some of the hollow cuts in the relief carving behind the cheek, this gun was carved pretty much entirely with my Pfeil V tool.