The kits mentioned by the others in this topic are similar in difficulty to the kits you've built in the past.
They are basically factory made guns that have not been totally finished.
The holes are pre-located and threaded where necessary. The parts are close to fitting although some may need small amounts of wood carefully trimmed away.
Basically, they are almost a "plug and play" kit.
If you take your time and ask questions in our Gun Builder's Bench area you will end up with a fine gun.
In case you are tempted to spend a bit more and buy one of the many "advanced kits" from places like Track of the Wolf, Pecatonica River, Chambers, Tennessee Valley Muzzleloading etc, you need to be aware that these are not the kind of kits you have done in the past.
The builder needs to have a good understanding of accurately laying out locations, drilling, threading, filing, chiseling and polishing to name just a few of the things that need to be known.
They are basically a box of totally unfinished castings and a roughed out stock blank.
You will have to locate, drill and thread screw holes, file and finish the rough castings and hand fit all of the parts.
The kind of kit you are thinking of takes from 15-30 hours to assemble if a good job is going to be done.
The "advanced kits" can easily take the builder 150 hours before the gun is finished.
(My first "advanced kit" took me over 180 hours).